**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
with create_session() as session:
            self.ti.state = state
            self.ti.try_number = try_number
            session.merge(self.ti)
        response = self.client.get(
            TestLogView.ENDPOINT, data=dict(username='test', password='test'), follow_redirects=True
        )
        self.assertEqual(response.status_code, 200)
        self.assertIn('Log by attempts', response.data.decode('utf-8'))
        for num in range(1, expected_num_logs_visible + 1):
            self.assertIn(f'log-group-{num}', response.data.decode('utf-8'))
        self.assertNotIn('log-group-0', response.data.decode('utf-8'))
        self.assertNotIn('log-group-{}'.format(expected_num_logs_visible + 1), response.data.decode('utf-8'))
    def test_get_logs_with_metadata_as_download_file(self):