Add AVIF support

[W-Floyd]

AVIF is efficient, well supported by browsers and can be embedded in GitHub markdown without any problems. I have implemented it in my fork for testing, and it works well.

[ShalokShalom]

Are you read to upstream it?

[W-Floyd]

I am, if it's approved. Given the PR template checks if:

I have created a discussion that was approved by a maintainer (for new features).

So I've been waiting for maintainer approval.