modules/autoupdate: add package diff to activationScripts

modules/autoupdate.nix

@@ -59,6 +59,15 @@
       randomizedDelaySec = "6h";
     };
 
+    # Always show a diff when activating a new system
+    system.activationScripts.diff-system = {
+      supportsDryActivation = true;
+      text = ''
+        echo System package diff:
+        ${config.nix.package}/bin/nix store diff-closures /run/current-system $systemConfig
+      '';
+    };
+
     environment.systemPackages = [ (
       # Provide a manual updating script that fetches the latest
       # updated+built system from Hydra