chore: add root build command

Author: Jannik Stehle

package.json

@@ -8,6 +8,8 @@
   "homepage": "https://github.com/owncloud/web-extensions",
   "type": "module",
   "scripts": {
+    "build": "pnpm -r build",
+    "build:w": "pnpm -r build:w",
     "check:types": "pnpm -r check:types",
     "lint": "eslint 'packages/**/*.{js,ts,vue}' --color",
     "test:unit": "pnpm -r test:unit",