`prePR` bot

[armanbilge]

Building on https://github.com/typelevel/sbt-typelevel/issues/15.

Assuming that we get our prePR command, I want a way to ask CI to run prePR for me and commit the changes.

I wonder if this can be accomplished (mostly) by spitting out an additional workflow. The only trick bit is figuring out how to conveniently trigger that workflow.

[armanbilge]

Something like this, for example. Run when a prePR label is added, which can be removed upon completion. https://docs.github.com/en/actions/managing-issues-and-pull-requests/commenting-on-an-issue-when-a-label-is-added

[rossabaker]

As long as it's opt-in, it could be useful.