fix: BigQuery job error message

[nathadfield]

closes: #34162

As mentioned on the issue, currently if a BigQuery job running in deferrable mode ends unsuccessfully during execution - perhaps by cancellation in the BigQuery UI or if the job runs out of resources - then the only message that is returned to logs is the rather unhelpful

[2023-09-08, 11:43:22 UTC] {taskinstance.py:1939} ERROR - Task failed with exception
Traceback (most recent call last):
  File "/opt/airflow/airflow/models/baseoperator.py", line 1613, in resume_execution
    return execute_callable(context)
  File "/opt/airflow/airflow/providers/google/cloud/operators/bigquery.py", line 2881, in execute_complete
    raise AirflowException(event["message"])
KeyError: 'message'

This is due to the fact that the async function get_job_status only returns the string error and the actual error message is left behind.

The change involved here is to return a dictionary object that contains both status and a message which, when a BQ job is in a DONE state but contains an errorResult, then the specific error is carried through.

This then results in the following error output when the job is cancelled from the UI.

[2023-09-08, 08:21:20 UTC] {taskinstance.py:1939} ERROR - Task failed with exception
Traceback (most recent call last):
  File "/opt/airflow/airflow/models/baseoperator.py", line 1613, in resume_execution
    return execute_callable(context)
  File "/opt/airflow/airflow/providers/google/cloud/operators/bigquery.py", line 2881, in execute_complete
    raise AirflowException(event["message"])
airflow.exceptions.AirflowException: Job execution was cancelled: User requested cancellation