**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

airflow/www/views.py
"""Mark Dag Blocked."""
        allowed_dag_ids = current_app.appbuilder.sm.get_accessible_dag_ids(g.user)
        
        selected_dag_ids = {unquote(dag_id) for dag_id in request.form.getlist('dag_ids') if dag_id}
        if selected_dag_ids:
            filter_dag_ids = selected_dag_ids.intersection(allowed_dag_ids)
        else:
            filter_dag_ids = allowed_dag_ids
        if not filter_dag_ids:
            return wwwutils.json_response([])
        
        dags = (
            session.query(DagRun.dag_id, sqla.func.count(DagRun.id))
            .filter(DagRun.state == State.RUNNING)
            .filter(DagRun.dag_id.in_(filter_dag_ids))
            .group_by(DagRun.dag_id)
        )
        
        payload = []
        for dag_id, active_dag_runs in dags:
            max_active_runs = 0
            dag = current_app.dag_bag.get_dag(dag_id)
            if dag:
                
                max_active_runs = dag.max_active_runs