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.

"""Next run info for dataset triggered DAGs."""
        allowed_dag_ids = get_airflow_app().appbuilder.sm.get_accessible_dag_ids(g.user)
        if not allowed_dag_ids:
            return flask.json.jsonify({})
        
        selected_dag_ids = {unquote(dag_id) for dag_id in request.form.getlist("dag_ids") if dag_id}
        if selected_dag_ids:
            filter_dag_ids = selected_dag_ids.intersection(allowed_dag_ids)
        else:
            filter_dag_ids = allowed_dag_ids
        dataset_triggered_dag_ids = [
            dag.dag_id
            for dag in session.query(DagModel.dag_id)
            .filter(DagModel.dag_id.in_(filter_dag_ids))
            .filter(DagModel.schedule_interval == "Dataset")
        ]
        dataset_triggered_next_run_info = get_dataset_triggered_next_run_info(
            dataset_triggered_dag_ids, session=session
        )
        return flask.json.jsonify(dataset_triggered_next_run_info)
    @expose("/dag_stats", methods=["POST"])
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG_RUN),
        ]
    )
    @provide_session
    def dag_stats(self, session: Session = NEW_SESSION):