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.

.join(DagScheduleDatasetReference, DagScheduleDatasetReference.dataset_id == DatasetModel.id)
                .join(
                    DatasetDagRunQueue,
                    and_(
                        DatasetDagRunQueue.dataset_id == DatasetModel.id,
                        DatasetDagRunQueue.target_dag_id == DagScheduleDatasetReference.dag_id,
                    ),
                    isouter=True,
                )
                .join(
                    DatasetEvent,
                    DatasetEvent.dataset_id == DatasetModel.id,
                    isouter=True,
                )
                .filter(DagScheduleDatasetReference.dag_id == dag_id, ~DatasetModel.is_orphaned)
                .group_by(DatasetModel.id, DatasetModel.uri)
                .order_by(DatasetModel.uri)
                .all()
            ]
        return (
            htmlsafe_json_dumps(data, separators=(",", ":"), dumps=flask.json.dumps),
            {"Content-Type": "application/json; charset=utf-8"},
        )
    @expose("/object/dataset_dependencies")
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG_DEPENDENCIES),
        ]
    )
    def dataset_dependencies(self):