To make current as default branch in private repo.

1. add the mirror workflow to current in public, add check on that it can be executed only on private repo.
2. Raise PR to public current and get that merged. (Gert this mirrored)
3. Update private repo default branch to current

Need to test this flow in test repos, and then will make this change in actual

Follow-up tasks (next):

1. Move mirror branch cleanup workflow to private reusable workflows
2. Update mirror trigger in public to use current as target trigger branch (instead of git-actions)