docs: Add documentation for enums (#336)

* docs: Add documentation for enums fix: Add context manager return types chore: Update gapic-generator-python to v1.8.1 PiperOrigin-RevId: 503210727 Source-Link: googleapis/googleapis@a391fd1 Source-Link: https://github.com/googleapis/googleapis-gen/commit/0080f830dec37c3384157082bce279e37079ea58 Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiMDA4MGY4MzBkZWMzN2MzMzg0MTU3MDgyYmNlMjc5ZTM3MDc5ZWE1OCJ9 * 🦉 Updates from OwlBot post-processor See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

google/cloud/container_v1/services/cluster_manager/client.py

@@ -4754,7 +4754,7 @@ def sample_list_usable_subnetworks():
  # Done; return the response.
  return response
 
- def __enter__(self):
+ def __enter__(self) -> "ClusterManagerClient":
  return self
 
  def __exit__(self, type, value, traceback):