message: Add clean script packages/theme
diff: "types": "dist/index.d.ts",
  "scripts": {
  "build": "backstage-cli plugin:build",
  - "lint": "backstage-cli lint"
  + "lint": "backstage-cli lint",
  + "clean": "backstage-cli clean"
  },
  "devDependencies": {
  "@backstage/cli": "^0.1.1-alpha.3",
  