message: Add clean script packages/app
diff: "scripts": {
  "start": "backstage-cli app:serve",
  "bundle": "backstage-cli app:build",
  + "clean": "backstage-cli clean",
  "test": "backstage-cli test",
  "test:e2e": "start-server-and-test start http://localhost:3000 cy:dev",
  "test:e2e:ci": "start-server-and-test start http://localhost:3000 cy:run",
  