Provide a list of taken approval rule names when the form is visible
### Problem to solve
When adding an approval rule, the entire form must be submitted to determine if the name is already taken or not.
### Intended users
Unknown / Anyone managing a project. Potentially any user with administrative rights to a project.
<!-- 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)
* [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-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)
* [Priyanka (Platform Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#priyanka-platform-engineer)
* [Dana (Data Analyst)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#dana-data-analyst)
-->
### User experience goal
The name field should respond to input by checking the value of the name field against a known list of taken names. That validation should appear where the current error appears, but without requiring that the form be submitted.
### Proposal
I propose that we add a small UX improvement to the front end that checks the value in the name field against a full list of known taken names. Providing the list of names to the form ahead of time would require new back end work to collect the names and deliver them - perhaps as an array - to the front end ahead of time (e.g. when the HTML is rendered). The front end can then check the name field against the provided list of taken names to show the validation error to the user without requiring that they submit the form, and without requiring any network traffic. The form would not be submittable with a duplicate name.
### Further details
This solution does introduce the possibility of a race condition: if the list of names is delivered to the front end, which has a long delay before submitting a new approval rule, a name may be taken already by another user in the system in the mean time. Then the user would be back to submitting the form and receiving an error, possibly leading them to even greater frustration since the UI was supposed to be telling them about taken names. This would be solved by https://gitlab.com/gitlab-org/gitlab/-/issues/251123, with the added cost of frequent network trips.
### Permissions and Security
<!-- 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 -->
### Documentation
<!-- 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/feature-change-workflow.html#documentation-requirements
* If this feature requires changing permissions, update the permissions document. See https://docs.gitlab.com/ee/user/permissions.html -->
### Availability & Testing
<!-- 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 test engineering planning process and reach out to your counterpart Software Engineer in Test for assistance: https://about.gitlab.com/handbook/engineering/quality/test-engineering/#test-planning -->
### What does success look like, and how can we measure that?
Success for this is zero approval rule submissions that result in an error indicating the name is taken **and** no complaints about invalid UI errors (like "this form says the name is taken but it's not!").
The overlap of those two data points means we're successfully preventing submissions with data we can know in advance will fail (and thus preventing user frustration with this experience) **and** we're not incorrectly blocking users from submitting data that is acceptable.
### What is the type of buyer?
<!-- 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/#four-tiers -->
### Is this a cross-stage feature?
<!-- 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 -->
### Links / references
<!-- Label reminders - you should have one of each of the following labels if you can figure out the correct ones -->
issue