**Description**
In the trigger page, there is a text area to enter (optional) conf json. It would be great if a sample JSON can be provided programatically while defining DAG

**Use case / motivation**

This will improve usability of the UI that triggers a DAG

tests/www/test_views.py
last_scheduler_heartbeat_for_testing_1 = timezone.utcnow()
        self.session.add(
            BaseJob(
                job_type='SchedulerJob',
                state='running',
                latest_heartbeat=last_scheduler_heartbeat_for_testing_1,
            )
        )
        self.session.commit()
        resp_json = json.loads(self.client.get('health', follow_redirects=True).data.decode('utf-8'))
        self.assertEqual('healthy', resp_json['metadatabase']['status'])
        self.assertEqual('healthy', resp_json['scheduler']['status'])
        self.assertEqual(
            last_scheduler_heartbeat_for_testing_1.isoformat(),
            resp_json['scheduler']['latest_scheduler_heartbeat'],
        )
        self.session.query(BaseJob).filter(
            BaseJob.job_type == 'SchedulerJob',
            BaseJob.state == 'running',
            BaseJob.latest_heartbeat == last_scheduler_heartbeat_for_testing_1,
        ).delete()
        self.session.commit()
        
        last_scheduler_heartbeat_for_testing_2 = timezone.utcnow() - timedelta(minutes=1)
        (