Add Usenet option

[TobiasB91]

Is your feature request related to a problem? Please describe.
I would like to use this single solution to manage my media server, but since I am not a torrent but a usenet user, I need to configure additional packages within nix.

Describe the solution you'd like
Since the transmission module is already part of this module, an option for usenet users would be appreciated. I'm not opinionated on any particular downloader, but there are options like sabnzbd or nzbget

Describe alternatives you've considered

Additional context

[rasmus-kirk]

Not opposed to this, but I won't personally implement it. You could use Nixarr for anything but usenet, and just add it manually to your nixos configuration, if you'd like.

[rlad78]

Really like the work y'all have done here @rasmus-kirk. I've had education and knowledge on usenet (cough) for many years now, so I might try to work on this. It would help me get more nix practice in as well c: