modules: services: nginx: overhaul modularity

This should be all that's needed for almost all my services.

machines/porthos/services.nix

@@ -90,6 +90,9 @@ in
       enable = true;
       password = my.secrets.nextcloud.password;
     };
+    nginx = {
+      enable = true; # FIXME: remove this when done migrating
+    };
     # The whole *arr software suite
     pirate.enable = true;
     # Podcast automatic downloader