**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
type(mock_log_reader.return_value).supports_read = PropertyMock(return_value=False)
        url_template = (
            "get_logs_with_metadata?dag_id={}&"
            "task_id={}&execution_date={}&"
            "try_number={}&metadata={}&format=json"
        )
        try_number = 1
        url = url_template.format(
            self.DAG_ID, self.TASK_ID, quote_plus(self.DEFAULT_DATE.isoformat()), try_number, json.dumps({})
        )
        response = self.client.get(url)
        self.assertEqual(200, response.status_code)
        self.assertIn('message', response.json)
        self.assertIn('metadata', response.json)
        self.assertIn('Task log handler does not support read logs.', response.json['message'])
    @parameterized.expand(
        [
            ('inexistent',),
            (TASK_ID,),
        ]
    )
    def test_redirect_to_external_log_with_local_log_handler(self, task_id):