**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 = 'graph?dag_id=example_bash_operator&execution_date={}'.format(
            self.percent_encode(self.EXAMPLE_DAG_DEFAULT_DATE)
        )
        resp = self.client.get(url, follow_redirects=True)
        self.check_content_in_response('runme_1', resp)
        
        self.session.commit()
        self.check_last_log(
            "example_bash_operator", event="graph", execution_date=self.EXAMPLE_DAG_DEFAULT_DATE
        )
    def test_action_logging_post(self):
        form = dict(
            task_id="runme_1",
            dag_id="example_bash_operator",
            execution_date=self.EXAMPLE_DAG_DEFAULT_DATE,
            upstream="false",
            downstream="false",
            future="false",
            past="false",
            only_failed="false",
        )
        resp = self.client.post("clear", data=form)
        self.check_content_in_response(['example_bash_operator', 'Wait a minute'], resp)
        
        self.session.commit()
        self.check_last_log(
            "example_bash_operator", event="clear", execution_date=self.EXAMPLE_DAG_DEFAULT_DATE
        )
class TestHelperFunctions(TestBase):