Add AVIF format support

[nczz]

Hi! Thanks for your awesome plugin!

Do you have plan to add AVIF format support at the future version?

[ddur]

Yes, in the future, but ...

1. Compared to WebP browser support , AVIF is still not well enough supported format.

2. Having WebP + another set of AVIF clones generated, may be to much disk space, for some users. So there will be probably a choice between WebP/AVIF format clones.

3. It is still unknown (to me) how to recognize AVIF compliant browsers in .htaccess, while image/webp in the HTTP_ACCEPT header is well established method to detect browsers supporting WebP images.

[ddur]

PHP 8.1: GD: AVIF image support