It's configured in the exact same way as other *arr apps, and thus
automatically gains the declarative port configuration now.
I also want to move the other two indexer modules under `servarr`, as
they are all closely related.
Let's consolidate all modules under one path, so that NixOS,
home-manager, and nix-darwin (if I ever end up using it down the line)
would go under the same folder.
