Introduce a direct way to require merge request for protected branches
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### Problem to solve
When I want to require everyone to submit merge requests for a protected branch, it is unclear on how to achieve this with the protected branches interface:

Coming from other platforms this could be done with a checkbox.
When looking at GitLab docs https://docs.gitlab.com/ee/user/project/protected_branches.html#require-everyone-to-submit-merge-requests-for-a-protected-branch, what needs to be done is to set the groups for allowed to push and allowed to merge:
- From the **Allowed to merge** list, select `Developers + Maintainers`.
- From the **Allowed to push** list, select `No one`.
### Proposal
The current way of setting up the requirement to use merge requests on a protected branch is indirect.
There should be a clear and direct way to enable the requirement to use merge requests on a protected branch. Some ideas are:
1. Add a checkbox or toggle, that says `Require merge requests on protected branches`
More ideas welcomed
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