Add avif and jxl image format support to Cloudflare Polish

Cloudflare has supported avif image format in Cloudflare Images, but not in Cloudflare Polish. There was an article in 2021 said avif would be supported soon, but in the ending of 2023, there is still no avif support.
[The article which mentioned avif support in 2021](https://blog.cloudflare.com/cloudflare-pages-ga/)

Additionally, jxl is a new royalty-free image format and has been supported since iOS 17, you can also add jxl support.

Cloudflare Polish Page: