message: add build to start script
diff: "name": "root",
  "private": true,
  "scripts": {
  - "start": "yarn workspace @spotify-backstage/app start",
  + "start": "yarn build && yarn workspace @spotify-backstage/app start",
  "build": "lerna run build",
  "test": "cross-env CI=true lerna run test --stream --parallel -- --coverage",
  "create-plugin": "yarn workspace @spotify-backstage/cli build && backstage-cli create-plugin",
  