**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
confirmed,
            upstream,
            downstream,
            future,
            past,
            State.FAILED,
        )
    @expose('/success', methods=['POST'])
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_TASK_INSTANCE),
        ]
    )
    @action_logging
    def success(self):
        """Mark task as success."""
        dag_id = request.form.get('dag_id')
        task_id = request.form.get('task_id')
        origin = get_safe_url(request.form.get('origin'))
        execution_date = request.form.get('execution_date')
        confirmed = request.form.get('confirmed') == "true"
        upstream = request.form.get('success_upstream') == "true"
        downstream = request.form.get('success_downstream') == "true"
        future = request.form.get('success_future') == "true"
        past = request.form.get('success_past') == "true"
        return self._mark_task_instance_state(
            dag_id,
            task_id,
            origin,