feat(services): add dedicated PostgreSQL module

Introduce a dedicated PostgreSQL configuration module to the system. Adjust Nextcloud and Forgejo configurations to utilize this new module.

systems/x86_64-linux/mx/default.nix

@@ -1,19 +1,20 @@
 { pkgs, lib, ... }:
 {
   imports = [
-    ./hardware-configuration.nix
-    ./rspamd.nix
     # ./goaccess.nix
-    ./nextcloud.nix
+    ./acme.nix
     ./backup.nix
-    ./users.nix
+    ./coturn.nix
+    ./forgejo.nix
+    ./hardware-configuration.nix
     ./kicker.nix
     ./mailserver.nix
-    ./acme.nix
-    ./forgejo.nix
-    ./nginx.nix
     ./network.nix
-    ./coturn.nix
+    ./nextcloud.nix
+    ./nginx.nix
+    ./postgresql.nix
+    ./rspamd.nix
+    ./users.nix
   ];
 
   metacfg = {