Mark MR as WIP when pushing WIP commits

What does this MR do?

It marks a merge request as WIP when you push commits to it that begin with wip: , squash! or fixup!. It does this by updating the MR's title to WIP: .., if it's not already marked as such.

Are there points in the code the reviewer needs to double check?

I have implemented work_in_progress? on Commit, to match MergeRequest, however a case could be made for just inlining this in the RefreshService, as the functionality is not used elsewhere and the functionality is kind of specific to this use case.

The tests for this rely on a wip branch existing that has at least one commit in it that matches the WIP rules for a commit (wip:, squash!, fixup!), so they will fail here.

Also, I'm sure that the test for the RefreshService could be cleaned up a bit, I'd love some pointers on that.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• [-] Documentation created/updated
• [-] API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #25036 (closed)