docs: mongodb api ref redirect (#29348)

docs/vercel.json

@@ -133,6 +133,10 @@
     {
       "source": "/docs/integrations/retrievers/weaviate-hybrid(/?)",
       "destination": "/docs/integrations/vectorstores/weaviate/#search-mechanism"
+    },
+    {
+      "source": "/api_reference/mongodb/:path(.*/?)*",
+      "destination": "https://langchain-mongodb.readthedocs.io/en/latest/langchain_mongodb/api_docs.html"
     }
   ]
 }