Add DevSecOpsApp code with updated Jenkins pipeline for multi-environment deployment

frontend/src/index.tsx

@@ -0,0 +1,14 @@
+import React from 'react';
+import ReactDOM from 'react-dom/client';
+import './index.css';
+import App from './App.tsx';
+
+const root = ReactDOM.createRoot(
+  document.getElementById('root') as HTMLElement
+);
+
+root.render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>
+);