feat(CustomizationService):Add a customization service (#2984)

* feat(customization):Add a customization service

Update UICustomizationService to v3-stable.

Also, adds an example customization for tab colors

* moved the customization service to ui category

extensions/default/src/getCustomizationModule.tsx

@@ -0,0 +1,29 @@
+import React from 'react';
+
+/**
+ *
+ * Note: this is an example of how the customization module can be used
+ * using the customization module. Below, we are adding a new custom route
+ * to the application at the path /custom and rendering a custom component
+ * Real world use cases of the having a custom route would be to add a
+ * custom page for the user to view their profile, or to add a custom
+ * page for login etc.
+ */
+export default function getCustomizationModule() {
+  return [
+    {
+      name: 'helloPage',
+      value: {
+        id: 'customRoutes',
+        routes: [
+          {
+            path: '/custom',
+            children: () => (
+              <h1 style={{ color: 'white' }}>Hello Custom Route</h1>
+            ),
+          },
+        ],
+      },
+    },
+  ];
+}