Add contributors image generation action

[skyash-dev]

#1
This introduces a reusable github action that generates a contributors image from the .all-contributorsrc file.

what it does:

• reads contributors from .all-contributorsrc
• fetches avatar images
• renders a grid image (contributors.png)
• commits the image to a dedicated branch
• opens a pull request automatically

implementation details:

• uses github api (octokit)
• handles branch creation and force updates to keep it in sync with base
• avoids duplicate PRs by checking existing ones
• separates image generation logic

tests:

• i have tested image generation logic locally.
• also tested octokit workflow on https://github.com/skyash-dev/test-contributors-png

GITHUB_TOKEN must be configured with the appropriate workflow permissions:

• enable read and write permissions
• enable allow github actions to create and approve pull requests

[skyash-dev]

@ksen0

[NalinDalal]

@skyash-dev i appreciate you doing this, not a maintainer but a fellow contributor.
Saw your message on discord, you have done an excellent work, but I feel that the code-logic can be optimised more.

Here are following points which i noticed on your code:

1. The action whenever runs unnecessarily uses github API, even if no changes are present; High chances of rate-limiting.
2. Image generation also can be optimised

• Re-downloads every avatar via fetch
• Re-renders the full canvas
• Re-encodes PNG
  This can be memoized I guess.

3. Force-Reset

You force-reset update-contributors-png to main every run:
updateRef(..., force: true)
This guarantees a new commit path even if nothing changed.

4. Compare previous and new image config
   There is no comparison between:

• existing contributors.png
• newly generated image
  So even identical output may still trigger a commit attempt.

5. PR logic
   You only avoid duplicate PRs, but you do not avoid redundant updates inside the branch.

---

What this means in practice:

• Unnecessary GitHub API usage
• Repeated avatar downloads (slow + rate limits risk)
• Wasted CI time
• Potential no-op commits if image content is identical

[NalinDalal]

Work can be more optimised for redundancy and other things.

[NalinDalal]

Silent failure (return null) may result in missing avatars without visibility. Consider logging failures (at least debug level) to help diagnose broken avatar URLs.

[skyash-dev]

i have tested the workflow multiple times and all images are successfully fetched consistently. and if in some case any fails, keeping that blank is a good default i think?

[skyash-dev]

@NalinDalal thank you for the review. funny how almost all fixes trace back to the same underlying issue (missing a comparison between contentBuffer and the existingBuffer).