Add an option to allow syncing with upstream even if nobody has rights to push and merge to a protected branch

Proposal

Issue

When creating a fork that I use to create merge requests to upstream, I like to fully lock up the master branch so that I don't accidentally push into that. Sadly this also locks up upstream syncing. To sync upstream you need to go the the settings and unlock the branch temporarily

Solution

Add an option to allow upstream syncing even if the branch is fully locked down. This is an option in github and it helps a lot. It reduces the need to go into the setting to unlock the branch temporarily