**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
"""
        Test that textarea in Trigger DAG UI is pre-populated
        with json config when the conf URL parameter is passed,
        or if a params dict is passed in the DAG
            1. Conf is not included in URL parameters -> DAG.conf is in textarea
            2. Conf is passed as a URL parameter -> passed conf json is in textarea
        """
        test_dag_id = "example_bash_operator"
        if not request_conf:
            resp = self.client.get(f'trigger?dag_id={test_dag_id}')
        else:
            test_request_conf = json.dumps(request_conf, indent=4)
            resp = self.client.get(f'trigger?dag_id={test_dag_id}&conf={test_request_conf}')
        expected_dag_conf = json.dumps(expected_conf, indent=4).replace("\"", "&#34;")
        self.check_content_in_response(
            f'<textarea class="form-control" name="conf">{expected_dag_conf}</textarea>', resp
        )
    def test_trigger_endpoint_uses_existing_dagbag(self):
        """
        Test that Trigger Endpoint uses the DagBag already created in views.py
        instead of creating a new one.
        """
        url = 'trigger?dag_id=example_bash_operator'
        resp = self.client.post(url, data={}, follow_redirects=True)
        self.check_content_in_response('example_bash_operator', resp)
class TestExtraLinks(TestBase):