GoogleVertexAISearchRetriever - AttributeError: 'ProtoType' object has no attribute 'DESCRIPTOR'
Labels: name: area: vector store, name: auto:bug

### System Info

Deployed on Cloud Run
```
Python 3.10
langchain                             0.0.345
langchain-cli                         0.0.19
langchain-core                        0.0.9
langchain-experimental                0.0.43
langdetect                            1.0.9
langserve                             0.0.32
langsmith                             0.0.69
```

```
google-ai-generativelanguage          0.3.3
google-api-core                       2.14.0
google-api-python-client              2.109.0
google-auth                           2.24.0
google-auth-httplib2                  0.1.1
google-auth-oauthlib                  1.1.0
google-cloud-aiplatform               1.36.4
google-cloud-bigquery                 3.13.0
google-cloud-core                     2.3.3
google-cloud-discoveryengine          0.11.3
google-cloud-pubsub                   2.18.4
google-cloud-resource-manager         1.10.4
google-cloud-storage                  2.13.0
google-crc32c                         1.5.0
google-generativeai                   0.2.2
google-resumable-media                2.6.0
googleapis-common-protos              1.61.0
```

Deployed via the Langchain template here:
https://github.com/langchain-ai/langchain/tree/master/templates/rag-google-cloud-vertexai-search

### Who can help?

@holtskinner I think has been fixing Google related stuff or knows someone who can

### Information

- [X] The official example notebooks/scripts
- [ ] My own modified scripts

### Related Components

- [ ] LLMs/Chat Models
- [ ] Embedding Models
- [ ] Prompts / Prompt Templates / Prompt Selectors
- [ ] Output Parsers
- [ ] Document Loaders
- [X] Vector Stores / Retrievers
- [ ] Memory
- [ ] Agents / Agent Executors
- [ ] Tools / Toolkits
- [ ] Chains
- [ ] Callbacks/Tracing
- [ ] Async

### Reproduction

Add https://github.com/langchain-ai/langchain/tree/master/templates/rag-google-cloud-vertexai-search to Langserve server

Run in playground with any input - get error.
AttributeError("'ProtoType' object has no attribute 'DESCRIPTOR'")

Langsmith chain:
```
{
  "id": [
    "langchain_core",
    "runnables",
    "RunnableSequence"
  ],
  "lc": 1,
  "type": "constructor",
  "kwargs": {
    "last": {
      "id": [
        "langchain_core",
        "output_parsers",
        "string",
        "StrOutputParser"
      ],
      "lc": 1,
      "type": "constructor",
      "kwargs": {}
    },
    "first": {
      "id": [
        "langchain_core",
        "runnables",
        "RunnableParallel"
      ],
      "lc": 1,
      "type": "constructor",
      "kwargs": {
        "steps": {
          "context": {
            "id": [
              "langchain",
              "retrievers",
              "google_vertex_ai_search",
              "GoogleVertexAISearchRetriever"
            ],
            "lc": 1,
            "repr": "GoogleVertexAISearchRetriever(project_id='project-id', data_store_id='datastore-id')",
            "type": "not_implemented"
          },
          "question": {
            "id": [
              "langchain_core",
              "runnables",
              "RunnablePassthrough"
            ],
            "lc": 1,
            "type": "constructor",
            "kwargs": {
              "func": null,
              "afunc": null,
              "input_type": null
            }
          }
        }
      }
    },
    "middle": [
      {
        "id": [
          "langchain_core",
          "prompts",
          "chat",
          "ChatPromptTemplate"
        ],
        "lc": 1,
        "type": "constructor",
        "kwargs": {
          "messages": [
            {
              "id": [
                "langchain_core",
                "prompts",
                "chat",
                "HumanMessagePromptTemplate"
              ],
              "lc": 1,
              "type": "constructor",
              "kwargs": {
                "prompt": {
                  "id": [
                    "langchain_core",
                    "prompts",
                    "prompt",
                    "PromptTemplate"
                  ],
                  "lc": 1,
                  "type": "constructor",
                  "kwargs": {
                    "template": "Answer the question based only on the following context:\n{context}\nQuestion: {question}\n",
                    "input_variables": [
                      "context",
                      "question"
                    ],
                    "template_format": "f-string",
                    "partial_variables": {}
                  }
                }
              }
            }
          ],
          "input_variables": [
            "context",
            "question"
          ]
        }
      },
      {
        "id": [
          "langchain",
          "chat_models",
          "vertexai",
          "ChatVertexAI"
        ],
        "lc": 1,
        "type": "constructor",
        "kwargs": {
          "model_name": "chat-bison",
          "temperature": 0
        }
      }
    ]
  }
}
```


The traceback comes back as:

```
  File "/usr/local/lib/python3.10/site-packages/langchain_core/retrievers.py", line 157, in _aget_relevant_documents
    return await asyncio.get_running_loop().run_in_executor(
  File "/usr/local/lib/python3.10/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/local/lib/python3.10/site-packages/langchain/retrievers/google_vertex_ai_search.py", line 343, in _get_relevant_documents
    search_request = self._create_search_request(query)
  File "/usr/local/lib/python3.10/site-packages/langchain/retrievers/google_vertex_ai_search.py", line 327, in _create_search_request
    return SearchRequest(
  File "/usr/local/lib/python3.10/site-packages/proto/message.py", line 570, in __init__
    pb_value = marshal.to_proto(pb_type, value)
  File "/usr/local/lib/python3.10/site-packages/proto/marshal/marshal.py", line 222, in to_proto
    proto_type.DESCRIPTOR.has_options
AttributeError: 'ProtoType' object has no attribute 'DESCRIPTOR'
```

### Expected behavior

The call to https://github.com/langchain-ai/langchain/blob/e1ea1912377ca7c013e89fac4c1d26c0cb836009/libs/langchain/langchain/retrievers/google_vertex_ai_search.py#L327

returns correctly with some documents.