Use webp by default

WebP look ready to roll though:
https://caniuse.com/?search=webp

Bringing this up as there seem to be some outstanding issues.

We should be much closer to making this conversion the default though.

This should really be addressed in 3.0.x first and then backported to 8.x-2.x if needed (especially since it's a feature request)

Created new MR targeting 3.0.x based on original MR