Add postgresql module

modules/databases/postgresql.nix

@@ -0,0 +1,38 @@
+{
+  config,
+  lib,
+  ...
+}:
+
+let
+  cfg = config.modules.databases.postgresql;
+in {
+  options.modules.databases.postgresql = {
+    enable = lib.mkOption {
+      default = false;
+      example = true;
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.postgresql = {
+      enable = true;
+      initdbArgs = [
+        "--allow-group-access"
+      ];
+      settings = {
+        log_connections = true;
+        log_disconnections = true;
+        log_destination = lib.mkForce "syslog";
+      };
+    };
+
+    services.borgmatic.settings = {
+      postgresql_databases = [
+        {
+          name = "all";
+        }
+      ];
+    };
+  };
+}