ci(playground): add bundle:watch script

Author: Niklas Kiefer

packages/form-js-playground/package.json

@@ -21,6 +21,7 @@
   "scripts": {
     "all": "run-s test build",
     "build": "rollup -c --failAfterWarnings",
+    "bundle:watch": "rollup -c -w --failAfterWarnings",
     "start": "SINGLE_START=basic npm run dev",
     "dev": "npm test -- --auto-watch --no-single-run",
     "test": "karma start",