**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
tis_to_clear += dr.get_task_instances()
            for dag, tis in dag_to_tis.items():
                cleared_ti_count += len(tis)
                models.clear_task_instances(tis, session, dag=dag)
            flash(
                "{count} dag runs and {altered_ti_count} task instances "
                "were cleared".format(count=count, altered_ti_count=cleared_ti_count)
            )
        except Exception:  
            flash('Failed to clear state', 'error')
        return redirect(self.get_default_url())
class LogModelView(AirflowModelView):
    """View to show records from Log table"""
    route_base = '/log'
    datamodel = AirflowModelView.CustomSQLAInterface(Log)  
    class_permission_name = permissions.RESOURCE_AUDIT_LOG
    method_permission_name = {
        'list': 'read',
    }
    base_permissions = [
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_ACCESS_MENU,
    ]
    list_columns = ['id', 'dttm', 'dag_id', 'task_id', 'event', 'execution_date', 'owner', 'extra']
    search_columns = ['dag_id', 'task_id', 'event', 'execution_date', 'owner', 'extra']
    base_order = ('dttm', 'desc')
    base_filters = [['dag_id', DagFilter, lambda: []]]
    formatters_columns = {
        'dttm': wwwutils.datetime_f('dttm'),
        'execution_date': wwwutils.datetime_f('execution_date'),