Passing number of stream in case of using bqstorage client

[nitishxp]

Hi,

I am using GCP batch to download the data from the BigQuery table using the bqStorage library

num_consumers = 2
iteratable = client.list_rows(bq_table_id)
iteratable._preserve_order = True // to ensure that only 1 read stream is created
for page in iteratable.to_arrow_iterable(bqstorage_client=client, max_queue_size=num_consumers * 2):
     data: list[dict] = [json.loads(json.dumps(d, default=str)) for d in page.to_pylist()]) // do something which Python object

The problem that I start to face is the number of threads spawned when _preserver_order is not set which causes it to spawn up to 128 threads in case using (e2-medium, e2-small) machine type hangs the program can we add an argument in the function to control the number of reads stream that we have.

eg:
for page in iteratable.to_arrow_iterable(bqstorage_client=client, max_queue_size=num_consumers * 2, no_of_stream=<>):