Factor out comment/upload feature from screenshot feature

[olivierdalang]

Hey ! Thanks a lot for this !

In my use case, I do not want to use the screenshoting part, since I already produce my own in my dockerized test suite (by the way, they are animated gifs, not images).

Unfortunately, this makes your action unusable. This is a shame since all the logic about upload service and calling the API works great.

I'd suggest factoring out the upload/comment part to a different action, usable on it's own. I've done this here: https://github.com/opengisch/comment-pr-with-images but of course happy to merge back / collaborate on this if you're interested maintaining a splitted version of your action.

Cheers.