Add annotations to protocol buffers indicating request parameters (via synth).

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/bigquery_storage/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
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Digest: sha256:70ba28fda87e032ae44e6df41b7fc342c1b0cce1ed90658c4890eb4f613038c2
Status: Downloaded newer image for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/bigquery/storage/artman_bigquerystorage_v1beta1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerystorage-v1beta1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/cloud/bigquery/storage/v1beta1/avro.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerystorage-v1beta1/google/cloud/bigquery_storage_v1beta1/proto/avro.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/cloud/bigquery/storage/v1beta1/table_reference.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerystorage-v1beta1/google/cloud/bigquery_storage_v1beta1/proto/table_reference.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/cloud/bigquery/storage/v1beta1/storage.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerystorage-v1beta1/google/cloud/bigquery_storage_v1beta1/proto/storage.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/cloud/bigquery/storage/v1beta1/read_options.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerystorage-v1beta1/google/cloud/bigquery_storage_v1beta1/proto/read_options.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigquerystorage-v1beta1/google/cloud/bigquery_storage_v1beta1/proto.
synthtool > Replaced 'from google.cloud.bigquery.storage_v1beta1.proto' in google/cloud/bigquery_storage_v1beta1/proto/storage_pb2.py.
synthtool > Replaced 'from google.cloud.bigquery.storage_v1beta1.proto' in google/cloud/bigquery_storage_v1beta1/proto/storage_pb2_grpc.py.
synthtool > Replaced 'google-cloud-bigquerystorage' in google/cloud/bigquery_storage_v1beta1/gapic/big_query_storage_client.py.
synthtool > Replaced 'import google.api_core.gapic_v1.method\n' in google/cloud/bigquery_storage_v1beta1/gapic/big_query_storage_client.py.
synthtool > Replaced 'from google.cloud import bigquery_storage_v1beta1' in tests/unit/gapic/v1beta1/test_big_query_storage_client_v1beta1.py.
synthtool > Replaced 'bigquery_storage_v1beta1.BigQueryStorageClient' in tests/unit/gapic/v1beta1/test_big_query_storage_client_v1beta1.py.
synthtool > Replaced 'if transport:' in google/cloud/bigquery_storage_v1beta1/gapic/big_query_storage_client.py.
synthtool > Replaced 'to_grpc_metadata\\(\\n' in google/cloud/bigquery_storage_v1beta1/gapic/big_query_storage_client.py.
synthtool > Replaced 'metadata.append\\(routing_metadata\\)' in google/cloud/bigquery_storage_v1beta1/gapic/big_query_storage_client.py.
synthtool > Replaced 'if channel is not None and credentials is not None:' in google/cloud/bigquery_storage_v1beta1/gapic/transports/big_query_storage_grpc_transport.py.
synthtool > Replaced 'if channel is None:' in google/cloud/bigquery_storage_v1beta1/gapic/transports/big_query_storage_grpc_transport.py.
synthtool > Replaced 'google.api_core.grpc_helpers.create_channel\\(' in google/cloud/bigquery_storage_v1beta1/gapic/transports/big_query_storage_grpc_transport.py.
Running session blacken
Creating virtualenv using python3.6 in /tmpfs/src/git/autosynth/working_repo/bigquery_storage/.nox/blacken
pip install --upgrade black
black google tests docs
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/gapic/big_query_storage_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/avro_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/gapic/transports/big_query_storage_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/read_options_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/read_options_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/avro_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/storage_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/table_reference_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/gapic/big_query_storage_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/types.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/table_reference_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/tests/unit/gapic/v1beta1/test_big_query_storage_client_v1beta1.py
reformatted /tmpfs/src/git/autosynth/working_repo/bigquery_storage/google/cloud/bigquery_storage_v1beta1/proto/storage_pb2.py
All done! ✨ 🍰 ✨
17 files reformatted, 12 files left unchanged.
Session blacken was successful.
synthtool > Cleaned up 0 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[tswast]

LGTM.

@crwilcox This PR looks pretty benign. No changes of any substance as far as I can tell. Do we just merge these PRs? What about the "[CHANGE ME]"?

[busunkim96]

@tswast Generally we modify the PR title (and commit message) to be a summary of the changes. #7511 is another Autosynth PR.