Add ability to turn off merge request approvals feature entirely
<!-- The first four sections: "Problem to solve", "Intended users", "User experience goal", and "Proposal", are strongly recommended, 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. --> ### Problem to solve As a user of the Core Omnibus edition of GitLab, I want to disable the merge request approval feature introduced to core in 13.2. The feature adds unnecessary UI bloat to the MR interface, and without the ability to define any rules in Core, it is completely superfluous to our needs. Typically these kinds of features can be disabled at the instance or project level, but after searching for such an ability I couldn't find it. The value added by making removing this feature configurable is streamlining the review screen when the approval workflow is not needed. ### Intended users Unknown as the goal is to _not_ use the approval feature. Configuration applied by administrators, simpler UI enjoyed by developers. ### User experience goal Simpler UI & merge request workflow when approvals are not needed. ### Proposal Enable a configuration option either in `gitlab.rb` for the instance, or a setting in the admin settings to disable MR approval entirely. Alternatively making this a project-level feature would be acceptable, but tedious. ### Further details N/A ### Permissions and Security N/A ### Documentation Documentation for instance configuration options would need updated. Feature documentation for MR approvals could be updated to mention the feature can be disabled by your admin. ### 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? - Ability to turn off MR approvals entirely - Once the feature is disabled, the MR UI should no longer show any approval-related elements ### What is the type of buyer? Cheapskates / smaller teams with simpler workflows. ### Is this a cross-stage feature? Not sure. ### Links / references <!-- Label reminders - you should have one of each of the following labels if you can figure out the correct ones -->
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