docs(iceberg): add iceberg user guide (#12533)

Author: chakru-r

docs-website/sidebars.js

@@ -919,6 +919,11 @@ module.exports = {
         },
       ],
     },
+    {
+      type: "doc",
+      id: "docs/iceberg-catalog",
+      label: "DataHub Iceberg REST Catalog",
+    },
     {
       "API & SDK Guides": [
         "docs/api/tutorials/datasets",