Update Branch button settings: allow choosing merge strategy

[6543]

come up in #9750 (comment)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. I am here to help clear issues left open even if solved or waiting for more insight. This issue will be closed if no further activity occurs during the next 2 weeks. If the issue is still valid just add a comment to keep it alive. Thank you for your contributions.

[6543]

ping

[6543]

closed by #16125