[feature] support webp in epub

[polyproline]

    WebP has many benefits over JPEG and PNG and while AVIF might eventually become a better option, it's probably a few years away from being widely adopted.
    Now webp is support in EPUB v3.3, in calibre 6.15.1, ebook-edit, ebook-viewer also support webp.

need to edit:
1. calibre.ebooks.oeb.polish.images.compress_images need to support png,jpg convert to webp
2. upgrade pillow to support webp, ebook-convert log
PIL\Image.py:3029: UserWarning: image file could not be identified because WEBP support not installed

past relative question:
https://bugs.launchpad.net/calibre/+bug/1922341
https://bugs.launchpad.net/calibre/+bug/2013104

[Kovid Goyal (kovid)]

Fixed in branch master. The fix will be in the next release. calibre is usually released every alternate Friday.