Branch protection: Require branches to be up to date before merging

[davidsvantesson]

Add a branch protection option allowing strict status checks. PR shall not be possible to merge unless it is up to date (divergence behind target is zero).

[guillep2k]

Sounds like this should be added to #8659 ... should I?

[zeripath]

Yeah add it

[6543]

hint: use function pull_service.GetDiverging(pull) added via #9784

[stale]

This issue has been automatically marked as stale because it has not had recent activity. I am here to help clear issues left open even if solved or waiting for more insight. This issue will be closed if no further activity occurs during the next 2 weeks. If the issue is still valid just add a comment to keep it alive. Thank you for your contributions.