nixos/cloud-init: Allow additional packages in cloud-init module

nixos/modules/services/system/cloud-init.nix

@@ -16,6 +16,7 @@ let
   ++ optional cfg.btrfs.enable btrfs-progs
   ++ optional cfg.ext4.enable e2fsprogs
   ++ optional cfg.xfs.enable xfsprogs
+  ++ cfg.extraPackages
   ;
   hasFs = fsName: lib.any (fs: fs.fsType == fsName) (lib.attrValues config.fileSystems);
   settingsFormat = pkgs.formats.yaml { };
@@ -79,6 +80,14 @@ in
         '';
       };
 
+      extraPackages = mkOption {
+        type = types.listOf types.package;
+        default = [ ];
+        description = ''
+          List of additional packages to be available within cloud-init jobs.
+        '';
+      };
+
       settings = mkOption {
         description = ''
           Structured cloud-init configuration.