**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
"""Autocomplete."""
        query = unquote(request.args.get('query', ''))
        if not query:
            wwwutils.json_response([])
        
        dag_ids_query = session.query(DagModel.dag_id.label('item')).filter(  
            ~DagModel.is_subdag, DagModel.is_active, DagModel.dag_id.ilike('%' + query + '%')
        )  
        owners_query = session.query(func.distinct(DagModel.owners).label('item')).filter(
            ~DagModel.is_subdag, DagModel.is_active, DagModel.owners.ilike('%' + query + '%')
        )  
        
        status = flask_session.get(FILTER_STATUS_COOKIE)
        if status == 'active':
            dag_ids_query = dag_ids_query.filter(~DagModel.is_paused)
            owners_query = owners_query.filter(~DagModel.is_paused)
        elif status == 'paused':
            dag_ids_query = dag_ids_query.filter(DagModel.is_paused)
            owners_query = owners_query.filter(DagModel.is_paused)
        filter_dag_ids = current_app.appbuilder.sm.get_accessible_dag_ids(g.user)
        
        dag_ids_query = dag_ids_query.filter(DagModel.dag_id.in_(filter_dag_ids))
        owners_query = owners_query.filter(DagModel.dag_id.in_(filter_dag_ids))
        
        payload = [row[0] for row in dag_ids_query.union(owners_query).limit(10).all()]
        return wwwutils.json_response(payload)