Training with a custom service account needs a new field named service account
trainingInput:
  serviceAccount: CUSTOM_SERVICE_ACCOUNT

https://cloud.google.com/ai-platform/training/docs/custom-service-account


airflow/providers/google/cloud/operators/mlengine.py
hook = MLEngineHook(
            gcp_conn_id=self._gcp_conn_id,
            delegate_to=self._delegate_to,
            impersonation_chain=self._impersonation_chain,
        )
        return hook.delete_model(
            project_id=self._project_id, model_name=self._model_name, delete_contents=self._delete_contents
        )
class MLEngineManageVersionOperator(BaseOperator):
    """
    Operator for managing a Google Cloud ML Engine version.
    .. warning::
       This operator is deprecated. Consider using operators for specific operations:
       MLEngineCreateVersionOperator, MLEngineSetDefaultVersionOperator,