[Implemented] Add support for av1 coding standard

[Mitzsch]

@Trishula

The desktop players should be capable if playing av1 due to mpv library, it’s the server that does not even allow direct stream of av1 files.

Exactly, well to be more precise only Plex for Desktop with a changed mpv lib is able to (direct) play av1 content.

Plex HTPC unfortunately does not do so (yet?) => Allow more codecs in the Plex HTPC profile