**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
"""Redirects to external log."""
        dag_id = request.args.get('dag_id')
        task_id = request.args.get('task_id')
        execution_date = request.args.get('execution_date')
        dttm = timezone.parse(execution_date)
        try_number = request.args.get('try_number', 1)
        ti = (
            session.query(models.TaskInstance)
            .filter(
                models.TaskInstance.dag_id == dag_id,
                models.TaskInstance.task_id == task_id,
                models.TaskInstance.execution_date == dttm,
            )
            .first()
        )
        if not ti:
            flash(f"Task [{dag_id}.{task_id}] does not exist", "error")
            return redirect(url_for('Airflow.index'))
        task_log_reader = TaskLogReader()
        if not task_log_reader.supports_external_link:
            flash("Task log handler does not support external links", "error")
            return redirect(url_for('Airflow.index'))
        handler = task_log_reader.log_handler
        url = handler.get_external_log_url(ti, try_number)
        return redirect(url)
    @expose('/task')