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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 -->


if self.append_job_name:
            self._append_uuid_to_job_name()
        def set_current_job(current_job):
            self.job = current_job
            DataflowJobLink.persist(self, context, self.project_id, self.location, self.job.get("id"))
        self.job = self.hook.start_flex_template(
            body=self.body,
            location=self.location,
            project_id=self.project_id,
            on_new_job_callback=set_current_job,
        )
        job_id = self.job.get("id")
        if job_id is None:
            raise AirflowException(
                "While reading job object after template execution error occurred. Job object has no id."
            )
        if not self.deferrable:
            return self.job
        self.defer(
            trigger=TemplateJobStartTrigger(
                project_id=self.project_id,
                job_id=job_id,
                location=self.location,
                gcp_conn_id=self.gcp_conn_id,
                impersonation_chain=self.impersonation_chain,
                cancel_timeout=self.cancel_timeout,
            ),
            method_name="execute_complete",
        )
    def _append_uuid_to_job_name(self):