adding modularity

utils/garbage-collection.nix

@@ -0,0 +1,23 @@
+{ lib, pkgs, ... }:
+
+{
+  # ...
+
+  # Limit the number of generations to keep
+  boot.loader.systemd-boot.configurationLimit = 10;
+  # boot.loader.grub.configurationLimit = 10;
+
+  # Perform garbage collection weekly to maintain low disk usage
+  nix.gc = {
+    automatic = true;
+    dates = "weekly";
+    options = "--delete-older-than 1w";
+  };
+
+  # Optimize storage
+  # You can also manually optimize the store via:
+  #    nix-store --optimise
+  # Refer to the following link for more details:
+  # https://nixos.org/manual/nix/stable/command-ref/conf-file.html#conf-auto-optimise-store
+  nix.settings.auto-optimise-store = true;
+}