The max number of response protos to put into each output JSON
file on GCS. The valid range is [1, 100]. If not specified,
the default value is 20. For example, for one pdf file with
100 pages, 100 response protos will be generated. If
batch_size = 20, then 5 json files each containing 20
response protos will be written under the prefix
gcs_destination.\ uri. Currently, batch_size only
applies to GcsDestination, with potential future support for
other output configurations.