**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
self.bash_dagrun = self.bash_dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=self.EXAMPLE_DAG_DEFAULT_DATE,
            start_date=timezone.utcnow(),
            state=State.RUNNING,
        )
        self.sub_dagrun = self.sub_dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=self.EXAMPLE_DAG_DEFAULT_DATE,
            start_date=timezone.utcnow(),
            state=State.RUNNING,
        )
        self.xcom_dagrun = self.xcom_dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=self.EXAMPLE_DAG_DEFAULT_DATE,
            start_date=timezone.utcnow(),
            state=State.RUNNING,
        )
    def check_last_log(self, dag_id, event, execution_date=None):
        from airflow.models import Log
        qry = self.session.query(Log.dag_id, Log.task_id, Log.event, Log.execution_date, Log.owner, Log.extra)
        qry = qry.filter(Log.dag_id == dag_id, Log.event == event)
        if execution_date:
            qry = qry.filter(Log.execution_date == execution_date)
        logs = qry.order_by(Log.dttm.desc()).limit(5).all()
        self.assertGreaterEqual(len(logs), 1)
        self.assertTrue(logs[0].extra)
    def test_action_logging_get(self):