Sonarr needs write access to the media directory so it can move the files after they've downloaded

[Fitzsimmons]

I used filesystem ACLs to give plex write access so that the frontend could be used to remove files. A similar technique can be used for sonarr.

[Fitzsimmons]

Media user (default justinf) also needs a default ACL for this since ownership will default to other users (e.g. sonarr) when they create directories that don't exist yet.