**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
permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_EDIT,
        permissions.ACTION_CAN_DELETE,
        permissions.ACTION_CAN_ACCESS_MENU,
    ]
    page_size = PAGE_SIZE
    list_columns = [
        'state',
        'dag_id',
        'task_id',
        'execution_date',
        'operator',
        'start_date',
        'end_date',
        'duration',
        'job_id',
        'hostname',
        'unixname',
        'priority_weight',
        'queue',
        'queued_dttm',
        'try_number',
        'pool',
        'queued_by_job_id',
        'external_executor_id',
        'log_url',
    ]
    order_columns = [
        item for item in list_columns if item not in ['try_number', 'log_url', 'external_executor_id']
    ]