add den pattern

modules/system/garbage-collection.nix

@@ -0,0 +1,17 @@
+{ config, lib, pkgs, ... }:
+
+let
+  dirModules = config.features.modules.system or { };
+in
+{
+  config = lib.mkIf ((dirModules.enable or false) && (dirModules.garbage-collection.enable or true)) {
+    nix = {
+      settings.auto-optimise-store = true;
+      gc = {
+        automatic = true;
+        dates = "weekly";
+        options = "--delete-older-than 7d";
+      };
+    };
+  };
+}