Add project configuration to require MRs to have the allow_collaboration flag set
Problem to solve
On projects that only accept FF merges and therefore generally require a rebase, receiving MRs that don't have the allow_collaboration flag set means that they can't be merged from GitLab itself without being manually rebased by committers and re-submitted in a new MR or pushed directly.
Target audience
Project maintainers who wants to rebase branches before merging them to avoid merge commits.
Proposal
Add a new configuration boolean to the project, something like "require_allow_collaboration_on_merge_requests". When it is set to true, when a developer wants to create a merge request, the "allow_collaboration" checkbox would be pre-ticked and greyed out with a message along the lines of "The maintainers of require that branches submitted as a merge request allow modifications, by submitting this merge request, you give them access to modify your branch."
What does success look like, and how can we measure that?
Maintainers of FF-only projects no longer receive merge requests that they can't merge because they can't rebase them.