chore(docs): add clean script for VitePress documentation build

Author: jspanchu

package.json

@@ -18,6 +18,7 @@
     "build": "npm run build:esm && npm run build:vtk && npm run build:viewer",
     "docs:build": "vitepress build docs",
     "docs:dev": "vitepress dev docs",
+    "docs:clean": "rimraf docs/.vitepress/dist",
     "docs:preview": "vitepress preview docs",
     "format": "prettier .  --write",
     "lint": "eslint --fix src",