**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={}"
        )
        response = self.client.get(
            url_template.format(
                self.DAG_ID, self.TASK_ID, quote_plus(self.DEFAULT_DATE.isoformat()), 1, json.dumps({})
            ),
            data=dict(username='test', password='test'),
            follow_redirects=True,
        )
        self.assertIn('"message":', response.data.decode('utf-8'))
        self.assertIn('"metadata":', response.data.decode('utf-8'))
        self.assertIn('Log for testing.', response.data.decode('utf-8'))
        self.assertEqual(200, response.status_code)
    def test_get_logs_with_null_metadata(self):