Added typescript types for react-dom demo app, added script for running backend test

Author: ngoczwolinski

demo-app/package.json

@@ -14,7 +14,7 @@
     "@types/express": "^4.17.13",
     "@types/node": "^17.0.8",
     "@types/react": "^17.0.38",
-    "@types/react-dom": "^17.0.11",
+    "@types/react-dom": "^17.0.19",
     "babel-loader": "^8.2.3",
     "copy-webpack-plugin": "^10.2.0",
     "css-loader": "^6.5.1",

demo-app/src/index.d.ts

@@ -0,0 +1,4 @@
+declare module 'react-dom/client' {
+  const ReactDOMClient: { createRoot: any };
+  export = ReactDOMClient;
+}