400 Error: "bigquery" output format does not support key_field in aiplatform_v1.BatchPredictionJob.InstanceConfig

## Summary
I encountered the following error when trying to specify the key_field in `aiplatform_v1.BatchPredictionJob.InstanceConfig` with a BigQuery input:
```
google.api_core.exceptions.InvalidArgument: 400 "bigquery" output format does not support key_field.
```

## Environment details

- OS type and version: `maxOS Sonoma 14.5`
- Python version: `3.11.10`
- `google-cloud-aiplatform` version: `1.69.0`

## Code example

```python
from google.cloud import aiplatform, aiplatform_v1

LOCATION = "asia-northeast1"
MY_PROJECT = "my-project"

def batch_predict_with_bq(
model: aiplatform.Model,
job_display_name: str,
bq_source_uri: str,
bq_output_uri: str,
machine_type: str,
) -> aiplatform_v1.BatchPredictionJob:
# https://cloud.google.com/python/docs/reference/aiplatform/latest/google.cloud.aiplatform_v1.types.BatchPredictionJob.InputConfig
input_config = aiplatform_v1.BatchPredictionJob.InputConfig(
instances_format="bigquery",
bigquery_source=aiplatform_v1.BigQuerySource(
input_uri=bq_source_uri,
),
)

# https://cloud.google.com/python/docs/reference/aiplatform/latest/google.cloud.aiplatform_v1.types.BatchPredictionJob.InstanceConfig
instance_config = aiplatform_v1.BatchPredictionJob.InstanceConfig(
excluded_fields=["user_id"],
key_field="key",
)

# https://cloud.google.com/python/docs/reference/aiplatform/latest/google.cloud.aiplatform_v1.types.BatchPredictionJob.OutputConfig
output_config = aiplatform_v1.BatchPredictionJob.OutputConfig(
predictions_format="bigquery",
bigquery_destination=aiplatform_v1.BigQueryDestination(
output_uri=bq_output_uri,
),
)

# https://cloud.google.com/python/docs/reference/aiplatform/latest/google.cloud.aiplatform_v1.types.BatchDedicatedResources
batch_dedicated_resources = aiplatform_v1.BatchDedicatedResources(
machine_spec=aiplatform_v1.MachineSpec(machine_type=machine_type),
starting_replica_count=1,
max_replica_count=1,
)

# https://cloud.google.com/python/docs/reference/aiplatform/latest/google.cloud.aiplatform_v1.types.BatchPredictionJob

job = aiplatform_v1.BatchPredictionJob(
name="test",
display_name=job_display_name,
model=model.resource_name,
input_config=input_config,
output_config=output_config,
instance_config=instance_config,
dedicated_resources=batch_dedicated_resources,
)

# https://cloud.google.com/python/docs/reference/aiplatform/latest/google.cloud.aiplatform_v1.services.job_service.JobServiceClient#google_cloud_aiplatform_v1_services_job_service_JobServiceClient_create_batch_prediction_job
client = aiplatform_v1.JobServiceClient(
client_options={"api_endpoint": f"{LOCATION}-aiplatform.googleapis.com"}
)

request = aiplatform_v1.CreateBatchPredictionJobRequest(
parent=f"projects/{MY_PROJECT}/locations/{LOCATION}",
batch_prediction_job=job,
)

response = client.create_batch_prediction_job(request=request)

return response

```

## Stack trace
```
The above exception was the direct cause of the following exception:

Traceback (most recent call last):

...
_ = batch_predict_with_bq(
^^^^^^^^^^^^^^^^^^^^^^
File "/Users/user/workspace/prog/python/vertexai/batch/main.py", line 305, in batch_predict_with_bq
response = client.create_batch_prediction_job(request=request)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/user/workspace/prog/python/vertexai/batch/.venv/lib/python3.11/site-packages/google/cloud/aiplatform_v1/services/job_service/client.py", line 3739, in create_batch_prediction_job
response = rpc(
^^^^
File "/Users/user/workspace/prog/python/vertexai/batch/.venv/lib/python3.11/site-packages/google/api_core/gapic_v1/method.py", line 131, in __call__
return wrapped_func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/user/workspace/prog/python/vertexai/batch/.venv/lib/python3.11/site-packages/google/api_core/grpc_helpers.py", line 78, in error_remapped_callable
raise exceptions.from_grpc_error(exc) from exc
google.api_core.exceptions.InvalidArgument: 400 "bigquery" output format does not support key_field.

```

## Expected Behavior
According to the [documentation](https://cloud.google.com/python/docs/reference/aiplatform/latest/google.cloud.aiplatform_v1.types.BatchPredictionJob.InstanceConfig), it seems that specifying `key_field` with a `bigquery` input should be allowed, but the error indicates otherwise.

## Actual Behavior
The job fails with a 400 error stating that the BigQuery output format does not support key_field, which contradicts the information in the documentation.

## Additional Information
If `key_field` is not supported for the `bigquery` format, it would be helpful to update the documentation to reflect this limitation. Otherwise, any guidance on resolving this issue would be greatly appreciated.

Thanks!