**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
resp = self.client.post('refresh?dag_id=example_bash_operator')
        self.check_content_in_response('', resp, resp_code=302)
    def test_refresh_all(self):
        with mock.patch.object(self.app.dag_bag, 'collect_dags_from_db') as collect_dags_from_db:
            resp = self.client.post("/refresh_all", follow_redirects=True)
            self.check_content_in_response('', resp)
            collect_dags_from_db.assert_called_once_with()
    def test_delete_dag_button_normal(self):
        resp = self.client.get('/', follow_redirects=True)
        self.check_content_in_response('/delete?dag_id=example_bash_operator', resp)
        self.check_content_in_response("return confirmDeleteDag(this, 'example_bash_operator')", resp)
    def test_delete_dag_button_for_dag_on_scheduler_only(self):
        
        
        
        dag_id = 'example_bash_operator'
        test_dag_id = "non_existent_dag"
        DM = models.DagModel  
        dag_query = self.session.query(DM).filter(DM.dag_id == dag_id)
        dag_query.first().tags = []  
        self.session.commit()
        dag_query.update({'dag_id': test_dag_id})
        self.session.commit()
        resp = self.client.get('/', follow_redirects=True)
        self.check_content_in_response(f'/delete?dag_id={test_dag_id}', resp)
        self.check_content_in_response(f"return confirmDeleteDag(this, '{test_dag_id}')", resp)
        self.session.query(DM).filter(DM.dag_id == test_dag_id).update({'dag_id': dag_id})
        self.session.commit()
    @parameterized.expand(["graph", "tree"])
    def test_show_external_log_redirect_link_with_local_log_handler(self, endpoint):