enable garbage collection

configuration.nix

@@ -81,6 +81,13 @@
   #   enableSSHSupport = true;
   # };
 
+  # Automatic Garbage Collection
+  nix.gc = {
+    automatic = true;
+    dates = "weekly";
+    options = "--delete-older-than 14d";
+  };
+
   # This value determines the NixOS release from which the default
   # settings for stateful data, like file locations and database versions
   # on your system were taken. It‘s perfectly fine and recommended to leave
@@ -88,5 +95,4 @@
   # Before changing this value read the documentation for this option
   # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
   system.stateVersion = "24.05"; # Did you read the comment?
-
 }