The DAGs main page has All/Active/Paused.

It would be nice if we can have also Running Now which will show all the DAGs that have at least 1 in Running of DAG runs:
![Screen Shot 2021-08-25 at 11 30 55](https://user-images.githubusercontent.com/62940116/130756490-647dc664-7528-4eb7-b4d8-515577f7e6bb.png)


For the above example the new DAGs tab of Running Now should show only 2 rows.
The use case is to see easily what DAGs are currently in progress.

"""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 = _safe_parse_datetime(execution_date)
        map_index = request.args.get("map_index", -1, type=int)
        try_number = request.args.get("try_number", 1)
        ti = (
            session.query(models.TaskInstance)
            .filter_by(dag_id=dag_id, task_id=task_id, execution_date=dttm, map_index=map_index)
            .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")
    @auth.has_access(