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**Description**

Related to the discussion here: https://github.com/apache/airflow/pull/8553#discussion_r416136954

Allow user to define expected terminal state. e.g. `JOB_STATE_CANCELLED` could be not treated as failure but expected terminal state.


<!-- A short description of your feature -->


trigger=TemplateJobStartTrigger(
                project_id=self.project_id,
                job_id=job_id,
                location=self.location if self.location else DEFAULT_DATAFLOW_LOCATION,
                gcp_conn_id=self.gcp_conn_id,
                poll_sleep=self.poll_sleep,
                impersonation_chain=self.impersonation_chain,
                cancel_timeout=self.cancel_timeout,
            ),
            method_name="execute_complete",
        )
    def execute_complete(self, context: Context, event: dict[str, Any]):
        """Method which executes after trigger finishes its work."""
        if event["status"] == "error" or event["status"] == "stopped":
            self.log.info("status: %s, msg: %s", event["status"], event["message"])
            raise AirflowException(event["message"])
        job_id = event["job_id"]
        self.log.info("Task %s completed with response %s", self.task_id, event["message"])
        return job_id
    def on_kill(self) -> None:
        self.log.info("On kill.")
        if self.job is not None:
            self.log.info("Cancelling job %s", self.job_name)
            self.hook.cancel_job(
                job_name=self.job_name,
                job_id=self.job.get("id"),
                project_id=self.job.get("projectId"),
                location=self.job.get("location"),
            )
class DataflowStartFlexTemplateOperator(GoogleCloudBaseOperator):