Option to enable pipelines must succeed at group level
### Problem to solve
Currently, you can prevent merge requests from being merged if the pipeline did not succeed. This is a [setting that is available at the project level](https://docs.gitlab.com/ee/user/project/merge_requests/merge_when_pipeline_succeeds.html#only-allow-merge-requests-to-be-merged-if-the-pipeline-succeeds). Maintainers are able to toggle this off at the project level, which has the effect of bypassing internal controls.
Regulated customers want the ability to ensure all pipelines are run and succeed before merging. The request is to add a "Pipelines must succeed" checkbox at the group level setting (only accessible by Group Owners), that cannot be overridden by the project level setting.
### Proposal
Use the [cascading framework](https://docs.gitlab.com/ee/development/cascading_settings.html#cascading-settings) to implement the pipeline must succeed merge check in groups/subgroups.
> Example: Checked and enforced at root group. Underlying subgroups and projects cannot uncheck. Projects can choose to allow skipped pipelines or not, but not if "Enforce pipelines must succeed" is enabled at the group level.
| Group 🔒 | Subgroup 🚫 | Project 🚫 |
| -------- | ----------- | ---------- |
|  |  |  |
|Success (Toast)|Failure (In-page alert)|Popover|
|---|---|---|
||||
### Intended users
* [Cameron (Compliance Manager)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#cameron-compliance-manager)
### Proposal
Similar to the [Disable self-approval at the instance level](https://gitlab.com/gitlab-org/gitlab/-/issues/39060), this proposal is asking for a "Pipelines must succeed" checkbox in the group area that takes precedence over any project-level "Pipelines must succeed" checkboxes. This should go under the `Group > Settings > General` screen.
### Implementation Plan
~backend https://gitlab.com/gitlab-org/gitlab/-/issues/373079+
~frontend :two: https://gitlab.com/gitlab-org/gitlab/-/issues/373080+
### Tier
gitlab~2278657
### Links / references
[Open Figma →](https://www.figma.com/file/BsjVjbYAr7Pi4RAFJGjIXI/%F0%9F%94%92-333135-Option-to-enable-pipelines-must-succeed-at-group-level?node-id=1832%3A16953)
epic