**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
self.session.query(BaseJob)
            .filter(BaseJob.job_type == 'SchedulerJob')
            .update({'latest_heartbeat': last_scheduler_heartbeat_for_testing_2 - timedelta(seconds=1)})
        )
        self.session.add(
            BaseJob(
                job_type='SchedulerJob',
                state='running',
                latest_heartbeat=last_scheduler_heartbeat_for_testing_2,
            )
        )
        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('unhealthy', resp_json['scheduler']['status'])
        self.assertEqual(
            last_scheduler_heartbeat_for_testing_2.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_2,
        ).delete()
        self.session.commit()
        
        self.session.query(BaseJob).filter(
            BaseJob.job_type == 'SchedulerJob', BaseJob.state == 'running'
        ).delete()
        self.session.commit()