Require postgres version to be configured manually

nixos-modules/postgresql/default.nix

@@ -12,6 +12,10 @@ with lib;
 {
   options.qois.postgresql = {
     enable = mkEnableOption ''Enable postgresql services with defaults'';
+    package = mkPackageOption pkgs "postgresql" {
+      example = "postgresql_15";
+      default = null;
+    };
   };
 
   config = mkIf cfg.enable {