add github action to implement #1490 contributor image

[kjhollen]

Implements @skyash-dev's solution from the p5.js repository:

• add a github action to generate the image in contributors-png.yml
  • add utils/contributors-png.js to use node & canvas to make an image
  • use processing-bot to generate a pull request with the new updated image when the all contributors file is changed
  • action only applies to processing/processing4 repo's main branch
• add contributors.png file with current list of contributors (generated during testing)
• make contributors.png visible in the README in the contributors section

[ksen0]

Definitely not a blocker: but potentially it's worth abstracting out both this and the p5 action into a separate action repo, like this one: https://github.com/processing/branch-pr-close-issue so the code is not duplicated in 2 places. @skyash-dev let me know if that would be of interest to you since you made the original action? I can make the repo and you could work on adding the action there and then updating the usages in processing4 and p5.js repos to use that.

[skyash-dev]

@ksen0 sounds good to me, happy to take this on.

[ksen0]

@skyash-dev great, thank you! I've made a repo here: https://github.com/processing/all-contributors-image/issues any of those are yours if you want them. I can only assign an issue after you comment on it. (You're welcome to suggest a new name for it as well)