Add custom 404 HTML page structure

Author: raghavs046

Modern Development/Service Portal Widgets/custom404/HTML.js

@@ -0,0 +1,10 @@
+<div>
+  <h1 class="heading-message">${This page could not be found. Based on your search we have found below valid pages}</h1>
+  <div class="page-container"> <!-- Container to show valid pages.-->
+    <ul>
+      <li ng-repeat="item in data.pageArr">  <!-- List to show valid pages.-->
+        <a href = {{item.url}} target="_blank">{{item.name}}</a>
+      </li>
+    </ul>
+  </div>
+</div>