chore: add prettier for code formatting

Author: lucarin91

package.json

@@ -3,7 +3,9 @@
   "version": "1.1.0",
   "description": "Node-RED nodes to talk to Arduino IoT Cloud",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "echo \"Error: no test specified\" && exit 1",
+    "fmt": "prettier --write .",
+    "fmt-check": "prettier --check ."
   },
   "keywords": [
     "node-red",
@@ -26,6 +28,9 @@
     "mqtt": "^3.0.0",
     "superagent": "^6.1.0"
   },
+  "devDependencies": {
+    "prettier": "^3.4.2"
+  },
   "repository": {
     "type": "git",
     "url": "git+https://github.com/arduino/node-red-contrib-arduino-iot-cloud.git"