chore(cI): allow PR autoformatting with a label

[theosanderson]

Expands our autoformatting workflow (previously just a workflow dispatch) so you can add the format_me label to a PR to have it autoformatted. Later we can get the formatting commits to use a PAT, and then they will trigger CI, which they don't atm.

[corneliusroemer]

Happy with this opt-in, don't see downsides right now other than even more commits on your branches 😆 Maybe just remember to clear the lengthy auto-generated commit messages when squash-merging your PRs.

[theosanderson]

Do we use commit bodies for anything atm?

[corneliusroemer]

Do we use commit bodies for anything atm?

They show in things like git log by default which I use regularly. That's where I see your *format *tweak's :)

[theosanderson]

OK, maybe I need to make an action to do merges for me to avoid that for you!