Add check for release branch to make sure local branch is synced with remote

Created by: marsblkm

• move branch check function to ensureBranchUpToDate() to make sure it can be done on any branch
• accomodate existing ensureMainBranchUpToDate()
• make sure release branch can be checked as well

Solve: https://github.com/sourcegraph/sourcegraph/issues/32783

Test plan

@marsblkm tested locally and manually by doing the following:

1. Checkout to branch 3.39 and randomly commit something (to simulate the scenario)
2. Checkout to main
3. Merge jm/check-local-and-remote-release-branch into main.
4. Set up dry run mode and execute yarn release release:create-candidate final