Port of 51725-push-mirrors-default-branch-reset-to-master to EE
What does this MR do?
Port changes in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21861 to EE.
What are the relevant issue numbers?
Does this MR meet the acceptance criteria?
Changelog entry added, if necessary
- Tests added for this feature/bug
- Conforms to the code review guidelines
- Conforms to the merge request performance guidelines
- Conforms to the style guides
Conforms to the database guides
EE specific content should be in the top level
- For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?