**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
name = 'no_response'
            def get_link(self, operator, dttm):  
                return None
        class FooBarLink(BaseOperatorLink):
            name = 'foo-bar'
            def get_link(self, operator, dttm):
                return 'http://www.example.com/{}/{}/{}'.format(operator.task_id, 'foo-bar', dttm)
        class AirflowLink(BaseOperatorLink):
            name = 'airflow'
            def get_link(self, operator, dttm):  
                return 'https://airflow.apache.org'
        class DummyTestOperator(BaseOperator):
            operator_extra_links = (
                RaiseErrorLink(),
                NoResponseLink(),
                FooBarLink(),
                AirflowLink(),
            )
        self.dag = DAG('dag', start_date=self.default_date)
        self.task = DummyTestOperator(task_id="some_dummy_task", dag=self.dag)
        self.task_2 = Dummy2TestOperator(task_id="some_dummy_task_2", dag=self.dag)
        self.task_3 = Dummy3TestOperator(task_id="some_dummy_task_3", dag=self.dag)
        self.app.dag_bag = mock.MagicMock(**{'get_dag.return_value': self.dag})
        super().setUp()
        self.logout()
        self.login('test_viewer', 'test_viewer')
    def test_extra_links_works(self):