Support AV1 itags

[B0pol]

YouTube provides AV1-encoded streams on some videos.

Example video: https://redirect.invidious.io/watch?v=kJQP7kiw5Fk

It seems like it's only available for videos with lots of views, probably because it requires more resources and their VCU ships don't support AV1 yet

AV1 gives us better quality and less bandwith needed.