**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
def setUp(self):
        from tests.test_utils.mock_operators import Dummy2TestOperator, Dummy3TestOperator
        self.endpoint = "extra_links"
        self.default_date = datetime(2017, 1, 1)
        class RaiseErrorLink(BaseOperatorLink):
            name = 'raise_error'
            def get_link(self, operator, dttm):
                raise ValueError('This is an error')
        class NoResponseLink(BaseOperatorLink):