Add button for removing source branch for merged MR's.
This allows the author (or any other with push access to the source repository) of a merge request to remove the source branch after the merge request has been merged.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
This allows the author (or any other with push access to the source repository) of a merge request to remove the source branch after the merge request has been merged.