[opus] support free WEBP images in Opus files

[Oliver Petry]

WebP (imagepart of VP9) is better then JPG
AVIF (imagepart of VPX/AV1) is better then HEIF

please support in OPUS file for album arts
more then JPG and PNG...

WebP and AVIF are free imageformats can store multiple images
thats good for the problem with METADATA_BLOCK_PICTURE
only can store one file.

i try to push some devs of player and converter to support this too.

wbr from berlin