feat: add context manager support in client (#8)

- [ ] Regenerate this pull request now.

chore: fix docstring for first attribute of protos

committer: @busunkim96
PiperOrigin-RevId: 401271153

Source-Link: googleapis/googleapis@787f8c9

Source-Link: googleapis/googleapis-gen@81decff
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiODFkZWNmZmU5ZmM3MjM5NmE4MTUzZTc1NmQxZDY3YTZlZWNmZDYyMCJ9

packages/google-cloud-common/google/cloud/common/types/operation_metadata.py

@@ -25,6 +25,7 @@
 
 class OperationMetadata(proto.Message):
     r"""Represents the metadata of the long-running operation.
+
     Attributes:
         create_time (google.protobuf.timestamp_pb2.Timestamp):
             Output only. The time the operation was