chore: add clean command

Author: aminya

package.json

@@ -11,6 +11,7 @@
     }
   },
   "scripts": {
+    "clean": "shx rm -rf ./_site* ./docs/_merged_*",
     "prestart": "npm run typedoc",
     "prebuild": "npm run tsc && npm run typedoc",
     "postinstall": "patch-package",
@@ -60,6 +61,7 @@
     "patch-package": "^6.4.7",
     "plugins-manager": "^0.2.1",
     "rollup-plugin-esbuild": "^3.0.2",
+    "shx": "^0.3.4",
     "typedoc": "^0.20.35",
     "typedoc-plugin-markdown": "^3.6.0",
     "typescript": "^4.2.3"