🐛 fix: thumbnailing animated webp

[CloudPassenger]

Related to issue #291 due to the lack of webp container support, so I integrated the go wrapper govips for using libvips to resize the animated webp

Updates:

• use prebuilt libwebp & libheif
• bump the version of the base docker image, it's now Alpine 3.20 (Docker image doesn't run on Alpine 3.19 #521)
• now use govips to decode webp, instead of golang.org/x/image
• use libvips to generate thumbnail for webp image (TODO: may alter imaging later)
• correctly support animated/non-animated thumbnails for animated webp image

[CloudPassenger]

Example:

animated-webp-emote-thumbnail.zip