services: add sabnzbd

Its configuration isn't declarative :-(.

Notably, the port needs to be changed from '8080' to '9090' in its
configuration file (at '/var/lib/sabnzbd/').

services/sabnzbd.nix

@@ -0,0 +1,28 @@
+# Usenet binary client.
+{ config, lib, ... }:
+let
+  cfg = config.my.services.sabnzbd;
+
+  domain = config.networking.domain;
+  sabnzbdDomain = "sabnzbd.${domain}";
+  port = 9090; # NOTE: not declaratively set...
+in
+{
+  options.my.services.sabnzbd = with lib; {
+    enable = mkEnableOption "SABnzbd binary news reader";
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.sabnzbd = {
+      enable = true;
+      group = "media";
+    };
+
+    services.nginx.virtualHosts."${sabnzbdDomain}" = {
+      forceSSL = true;
+      useACMEHost = domain;
+
+      locations."/".proxyPass = "http://localhost:${toString port}";
+    };
+  };
+}