**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
url_template = (
            "get_logs_with_metadata?dag_id={}&"
            "task_id={}&execution_date={}&"
            "try_number={}&metadata={}&format=file"
        )
        try_number = 1
        url = url_template.format(
            self.DAG_ID,
            'Non_Existing_ID',
            quote_plus(self.DEFAULT_DATE.isoformat()),
            try_number,
            json.dumps({}),
        )
        response = self.client.get(url)
        self.assertIn('message', response.json)
        self.assertIn('error', response.json)
        self.assertEqual("*** Task instance did not exist in the DB\n", response.json['message'])
    def test_get_logs_with_json_response_format(self):