Add an automated PR comment

[junedev]

Angelika created this great GitHub action that can generate PR comments depending on which files have changed in the PR.
https://github.com/exercism/pr-commenter-action

An example can be seen in the Elixir Track: exercism/elixir#930 (comment)

I was thinking about adding something similar for the JavaScript track.
It could take care of the following things:

• Remind the maintainer to set the correct size label.
• If concept about.md, introduction.md or exercise introduction.md for a concept exercise is changed, remind the contributor to check the change is applied consistently to all 3 files.
• If the exemplar or the stub is changed, remind the contributor to check that both files are kept in sync (same JSDoc comments, same function signatures).
• If a practice exercise introduction or test file is changed, remind the contributor to check whether the exercise originates in problem-spec and what to do in that case.

Any objections? Any thoughts on additional things the PR comment should cover?

[SleeplessByte]

here I things I don't know if possible

• if core-js is updated, babel.config.js must too
• if instructions.md of a practice exercise, remind them that only the file may be regenerated and the rest must be in appends (slightly different than what was listed)
• some more info for maintainers?

[junedev]

@SleeplessByte

if core-js is updated, babel.config.js must too

If I remember correctly this is covered by a CI check now.

if instructions.md of a practice exercise, remind them that only the file may be regenerated and the rest must be in appends (slightly different than what was listed)

I was told recently that configlet sync does not work for instructions (the PR is still draft with lots of todos exercism/configlet#366) so I am not sure what you are referring to here when you say "regenerated".

[SleeplessByte]

Right. Yes. You are right. I meant that for practice exercises, the instructions should be like canonical, and only appends should be used to add things...