CI: add slash dispatch workflow to trigger pre-commit checks with comment
This would be an on-demand bot to run pre-commit checks on a PR, which can be triggered by commenting

```
@github-actions pre-commit
```

on a pull request (see [here](https://github.com/nbQA-dev/nbQA/pull/518) for a demo).

Use case: if a PR is submitted and is good-to-go except for some linting error, we can just comment `/pre-commit-run` and have the bot fixup the errors.
Cool, thanks! 
That actually reminded me that we use something similar in the arrow repo, using comments to trigger actions: https://github.com/apache/arrow/blob/master/.github/workflows/comment_bot.yml. This seems to check the content of the comment, instead of using one workflow (with slash-command-dispatch) to trigger another, which seems a bit simpler to me? Thanks @jorisvandenbossche ! I didn't know you could do that, that indeed does look simpler, I'll see if I can update this to do it that way @jorisvandenbossche OK, done

If the comment-bot is now largely taken from `arrow`, my understanding is that we need to include their license at the top of the file - is this right? > If the comment-bot is now largely taken from arrow, my understanding is that we need to include their license at the top of the file - is this right?

I don't think that that is necesaarily needed in this case. I mean, I contribute to several projects, and I am constantly applying what I tried / learned how to set up github actions in one project to other projects. Also, if you include the license, you would need to clearly state what has changed. And in the end, the main thing you copied is the line `if: startsWith(github.event.comment.body, '@github-actions autotune')` and the idea to use the pr-push action, for the rest it's a lot different compared to the original file from arrow. What are your thoughts on https://github.com/pandas-dev/pandas/pull/38444#issuecomment-746988296 ? Hey Joris - sorry, I missed that comment, somehow my brain only registered the review comments - I've removed the license header as I think your assessment makes perfect sense (as someone with far less experience, I was trying to tread carefully) this looks fine to me. let's give it a try. @MarcoGorelli can you add somewhere the various actions that are availabel (take is in the user docs, but this one plus the backport ones could go somewhere) Thanks!