Merge requests merged outside GitLab should self-resolve
### Problem to solve
Merge requests that are obsolete because they have been merged already should auto-close
### Further details
Samba is slowly moving to GitLab, but for now while we accept merge requests, these are not merged with the UI, but offline via a git push to our master repository (after further automated testing). The patches are rebased and fast-forwarded onto the (eg master) branch.
This means that Samba developers need to manually update merge requests with the details of where they ended up, and close them.
eg https://gitlab.com/samba-team/samba/merge_requests/55
This seems a good job for a computer, particularly as ability to merge is being checked each time master is updated.
### Proposal
Automatically include text showing when the patch appears to have been merged, and close the request as resolved.
### What does success look like, and how can we measure that?
Offline rebase merges of patches trigger the closure of issues without human intervention.
### Links / references
issue