services: move 'media' to 'modules' instead

Its not actually a service, but more of a configuration needed by some
services. Therefore it belongs in modules.

modules/default.nix

@@ -5,6 +5,7 @@
   imports = [
     ./ergodox.nix
     ./language.nix
+    ./media.nix
     ./networking.nix
     ./nix.nix
     ./packages.nix

modules/media.nix

@@ -0,0 +1,16 @@
+# Abstracting away the need for a common 'media' group
+
+{ config, lib, ... }:
+let
+  mediaServices = with config.my.services; [
+    calibre-web
+    jellyfin
+    pirate
+    sabnzbd
+    transmission
+  ];
+  needed = builtins.any (service: service.enable) mediaServices;
+in
+{
+  config.users.groups.media = lib.mkIf needed { };
+}