Rebase workflow

This describes the high-level workflow to rebase our Redash fork on top of the recent master of upstream Redash.

1. Fetch remote from upstream
2. Create tracking branch mXX-rebase from upstream master
3. Fetch latest changes from mozilla master
4. Open list of commits in mozilla master in browser
5. Look for last commit that wasn’t one of the upstream commits
6. Cherry-pick commits individually, when needed (e.g. feature may have been ported or become moot)
7. Keep notes which commits have been applied, applied with extra TODOs (e.g. let OPs do something), dropped or dropped but with extra TODOs
8. Review all applied commits and see if any can be collapsed.
9. Collapse commits by rebasing interactively on top of upstream master.
10. Note collapsed commits in notes.
11. Review TODOs and open follow-up tickets.
12. Push mXX-rebase branch to fork repo.
13. Open PR between mXX-rebase and release branches in fork repo with notes as PR description.
14. Ask peers to do rebase review.
15. Fix issues if needed.
16. Collapse fixes again if needed.
17. Force push mXX-rebase branch to release branch.
18. Review rc environment.