Properly quote environment variables

Update official catalog items for 21.04

Update feature capability to add recent validation refs

Automatically add nvidia env variable when nvidia gpu is configured for plex

Update plex probes

Add BSD License

After testing on 21.02-ALPHA it seems like 21.02-ALPHA doesn't actually support the definitions/certificate and definitions/certificateAuthority very well (if at all).

Setting the stable to 21.04-ALPHA seems okey, while it isn't officially a planned release, it can always be adapted to the actual release date in the future.

The link to the upstream Helm Chart Developer Reference is broken (404), this is the right link.

Allow running privileged containers