Turn on auto-optimize nix store to save disk space on staging

morph/lib/issuer-aws.nix

@@ -32,4 +32,8 @@
     dates = "weekly";
     options = "--delete-older-than 30d";
   };
+
+  # Turn on automatic optimization of nix store
+  # https://nixos.wiki/wiki/Storage_optimization
+  nix.autoOptimiseStore = true;
 }