added json.loads() to convert user_metadata to json

examples/vertex_ai_conversation/evaluation_tool__autoeval__colab.ipynb

@@ -804,6 +804,13 @@
         "      ) -> VertexConversationResponse:\n",
         "    if session_id is None:\n",
         "      session_id = self.sessions.build_session_id(self.agent_id)\n",
+        "\n",
+        "    if user_metadata:\n",
+        "      try:\n",
+        "        user_metadata = json.loads(user_metadata)\n",
+        "      except ValueError as err:\n",
+        "        raise UserWarning(\"Invalid user metadata\") from err\n",
+        "  \n",
         "    response = self.detect_intent(\n",
         "        agent_id=self.agent_id,\n",
         "        session_id=session_id,\n",