feat: Add service_account_id output field to CloudSQL properties (#237)

- [ ] Regenerate this pull request now.

Clients can now observe the Service Account that is being used when connecting to the CloudSQL from the BigQuery.

PiperOrigin-RevId: 463445598

Source-Link: googleapis/googleapis@fe833dd

Source-Link: https://github.com/googleapis/googleapis-gen/commit/73fad9a6502225fc64332b2f6fea8089cda6db55
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiNzNmYWQ5YTY1MDIyMjVmYzY0MzMyYjJmNmZlYTgwODljZGE2ZGI1NSJ9

google/cloud/bigquery_connection_v1/types/connection.py

@@ -294,6 +294,14 @@ class CloudSqlProperties(proto.Message):
             Type of the Cloud SQL database.
         credential (google.cloud.bigquery_connection_v1.types.CloudSqlCredential):
             Input only. Cloud SQL credential.
+        service_account_id (str):
+            Output only. The account ID of the service
+            used for the purpose of this connection.
+            When the connection is used in the context of an
+            operation in BigQuery, this service account will
+            serve as identity being used for connecting to
+            the CloudSQL instance specified in this
+            connection.
     """
 
     class DatabaseType(proto.Enum):
@@ -320,6 +328,10 @@ class DatabaseType(proto.Enum):
         number=4,
         message="CloudSqlCredential",
     )
+    service_account_id = proto.Field(
+        proto.STRING,
+        number=5,
+    )
 
 
 class CloudSqlCredential(proto.Message):