Add configuration to include/exclude GitLab provided built-in templates from end users on a self-managed GitLab instance
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=375286)
</details>
<!--IssueSummary end-->
<!-- The first section "Release notes" is required if you want to have your release post blog MR auto generated. Currently in BETA, details on the **release post item generator** can be found in the handbook: https://about.gitlab.com/handbook/marketing/blog/release-posts/#release-post-item-generator and this video: https://www.youtube.com/watch?v=rfn9ebgTwKg. The next four sections: "Problem to solve", "Intended users", "User experience goal", and "Proposal", are strongly recommended in your first draft, while the rest of the sections can be filled out during the problem validation or breakdown phase. However, keep in mind that providing complete and relevant information early helps our product team validate the problem and start working on a solution. -->
<!-- What is the problem and solution you're proposing? This content sets the overall vision for the feature and serves as the release notes that will populate in various places, including the [release post blog](https://about.gitlab.com/releases/categories/releases/) and [Gitlab project releases](https://gitlab.com/gitlab-org/gitlab/-/releases). " -->
### Problem to solve
Some customers create their own self-managed templates for end-users to choose from and do not want the end-users to confuse the Instance level templates with the built-in templates provided by GitLab. To ease confusion on self-managed instances that use this strategy, we propose to add a configuration to exclude GitLab provided templates from the UI. Only GitLab admins will have the ability to turn this feature on or off.
(I would expect to see this at an organization where customers require a certain type of authentication. For example, assume a customer builds a Spring template that includes a unique authentication method, and they require all projects using Spring to use this Spring template. There would be no reason to even include the GitLab provided Spring template.)
<!-- What problem do we solve? Try to define the who/what/why of the opportunity as a user story. For example, "As a (who), I want (what), so I can (why/value)." -->
### Intended users
GitLab Systems Administrator
<!-- Who will use this feature? If known, include any of the following: types of users (e.g. Developer), personas, or specific company roles (e.g. Release Manager). It's okay to write "Unknown" and fill this field in later.
Personas are described at https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/
* [Cameron (Compliance Manager)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#cameron-compliance-manager)
* [Parker (Product Manager)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#parker-product-manager)
* [Delaney (Development Team Lead)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#delaney-development-team-lead)
* [Presley (Product Designer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#presley-product-designer)
* [Sasha (Software Developer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer)
* [Priyanka (Platform Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#priyanka-platform-engineer)
* [Sidney (Systems Administrator)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sidney-systems-administrator)
* [Sam (Security Analyst)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sam-security-analyst)
* [Rachel (Release Manager)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#rachel-release-manager)
* [Alex (Security Operations Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#alex-security-operations-engineer)
* [Simone (Software Engineer in Test)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#simone-software-engineer-in-test)
* [Allison (Application Ops)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#allison-application-ops)
* [Ingrid (Infrastructure Operator)](https://about.gitlab.com/handbook/product/personas/#ingrid-infrastructure-operator)
* [Dakota (Application Development Director)](https://about.gitlab.com/handbook/product/personas/#dakota-application-development-director)
* [Dana (Data Analyst)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#dana-data-analyst)
* [Eddie (Content Editor)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#eddie-content-editor)
-->
### User experience goal
The GitLab System Administrator should be able to use the [Admin Area Templates UI](https://docs.gitlab.com/ee/user/admin_area/settings/#templates) to configure the GitLab Self-Managed Instance to include or exclude the GitLab provided built-in templates.
<!-- What is the single user experience workflow this problem addresses?
For example, "The user should be able to use the UI/API/.gitlab-ci.yml with GitLab to <perform a specific task>"
https://about.gitlab.com/handbook/product/ux/ux-research-training/user-story-mapping/ -->
### Proposal
<!-- How are we going to solve the problem? Try to include the user journey! https://about.gitlab.com/handbook/journeys/#user-journey -->
Add a configuration flag to include/exclude the built-in templates view from the UI. We do NOT need to remove the templates, we just need to hide them which should be solvable from a UI perspective.
### Further details
This will be useful for companies/agencies in highly-regulated industries. Many times, highly-regulated industries will have a requirement for an application to be behind some sort of authentication service that is company-provided, often times legacy. In these cases, companies may build on top of GitLab provided templates to create their own for their organization. To avoid confusion, they would want to exclude the built-in templates to their end-users.
<!-- Include use cases, benefits, goals, or any other details that will help us understand the problem better. -->
### Permissions and Security
Only (self-managed) GitLab Administrators would have the ability to turn built-in templates on/off.
<!-- What permissions are required to perform the described actions? Are they consistent with the existing permissions as documented for users, groups, and projects as appropriate? Is the proposed behavior consistent between the UI, API, and other access methods (e.g. email replies)?
Consider adding checkboxes and expectations of users with certain levels of membership https://docs.gitlab.com/ee/user/permissions.html
* [ ] Add expected impact to members with no access (0)
* [ ] Add expected impact to Guest (10) members
* [ ] Add expected impact to Reporter (20) members
* [ ] Add expected impact to Developer (30) members
* [ ] Add expected impact to Maintainer (40) members
* [ ] Add expected impact to Owner (50) members
Please consider performing a threat model for the code changes that are introduced as part of this feature. To get started, refer to our Threat Modeling handbook page https://about.gitlab.com/handbook/security/threat_modeling/#threat-modeling.
Don't hesitate to reach out to the Application Security Team (`@gitlab-com/gl-security/appsec`) to discuss any security concerns.
-->
### Documentation
Assuming this feature is added, we would need to make changes to the following documentation:
- https://docs.gitlab.com/ee/user/admin_area/settings/#templates
<!-- See the Feature Change Documentation Workflow https://docs.gitlab.com/ee/development/documentation/workflow.html#for-a-product-change
* Add all known Documentation Requirements in this section. See https://docs.gitlab.com/ee/development/documentation/workflow.html
* If this feature requires changing permissions, update the permissions document. See https://docs.gitlab.com/ee/user/permissions.html -->
### Availability & Testing
Unknown
<!-- This section needs to be retained and filled in during the workflow planning breakdown phase of this feature proposal, if not earlier.
What risks does this change pose to our availability? How might it affect the quality of the product? What additional test coverage or changes to tests will be needed? Will it require cross-browser testing?
Please list the test areas (unit, integration and end-to-end) that needs to be added or updated to ensure that this feature will work as intended. Please use the list below as guidance.
* Unit test changes
* Integration test changes
* End-to-end test change
See the Quality Engineering quad planning and test planning processes and reach out to your counterpart Software Engineer in Test for assistance.
Quad Planning: https://about.gitlab.com/handbook/engineering/quality/quality-engineering/quad-planning
Test Planning: https://about.gitlab.com/handbook/engineering/quality/quality-engineering/test-engineering/#test-planning -->
### Available Tier
Premium (Self-Managed)
<!-- This section should be used for setting the appropriate tier that this feature will belong to. Pricing can be found here: https://about.gitlab.com/pricing/
* Free
* Premium/Silver
* Ultimate/Gold
-->
### Feature Usage Metrics
Unknown
<!-- How are you going to track usage of this feature? Think about user behavior and their interaction with the product. What indicates someone is getting value from it?
Create tracking issue using the Snowplow event tracking template. See https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Snowplow%20event%20tracking.md
-->
### What does success look like, and how can we measure that?
Unknown
<!--
Define both the success metrics and acceptance criteria. Note that success metrics indicate the desired business outcomes, while acceptance criteria indicate when the solution is working correctly. If there is no way to measure success, link to an issue that will implement a way to measure this.
Create tracking issue using the Snowplow event tracking template. See https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Snowplow%20event%20tracking.md
-->
### What is the type of buyer?
CISO, CIO, VP of App Dev
<!-- What is the buyer persona for this feature? See https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/buyer-persona/
In which enterprise tier should this feature go? See https://about.gitlab.com/handbook/product/pricing/#three-tiers -->
### Is this a cross-stage feature?
No
<!-- Communicate if this change will affect multiple Stage Groups or product areas. We recommend always start with the assumption that a feature request will have an impact into another Group. Loop in the most relevant PM and Product Designer from that Group to provide strategic support to help align the Group's broader plan and vision, as well as to avoid UX and technical debt. https://about.gitlab.com/handbook/product/#cross-stage-features -->
### What is the competitive advantage or differentiation for this feature?
This will be advantageous for any highly-regulated industry, in particular, the US Public Sector.
### Links / references
<!-- Label reminders - you should have one of each of the following labels.
Use the following resources to find the appropriate labels:
- https://gitlab.com/gitlab-org/gitlab/-/labels
- https://about.gitlab.com/handbook/product/categories/features/
-->
issue