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.

"executor_class",
        "hostname",
        "unixname",
    ]
    base_order = ("start_date", "desc")
    base_filters = [["dag_id", DagFilter, lambda: []]]
    formatters_columns = {
        "start_date": wwwutils.datetime_f("start_date"),
        "end_date": wwwutils.datetime_f("end_date"),
        "hostname": wwwutils.nobr_f("hostname"),
        "state": wwwutils.state_f,
        "latest_heartbeat": wwwutils.datetime_f("latest_heartbeat"),
    }
class DagRunModelView(AirflowPrivilegeVerifierModelView):
    """View to show records from DagRun table."""
    route_base = "/dagrun"
    datamodel = wwwutils.DagRunCustomSQLAInterface(models.DagRun)  
    class_permission_name = permissions.RESOURCE_DAG_RUN
    method_permission_name = {
        "list": "read",
        "action_clear": "edit",
        "action_muldelete": "delete",
        "action_set_queued": "edit",
        "action_set_running": "edit",
        "action_set_failed": "edit",
        "action_set_success": "edit",
    }
    base_permissions = [
        permissions.ACTION_CAN_CREATE,
        permissions.ACTION_CAN_READ,