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.

method_permission_name = {
        "list": "read",
    }
    base_permissions = [
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_ACCESS_MENU,
    ]
    list_columns = ["id", "dttm", "dag_id", "task_id", "event", "execution_date", "owner", "extra"]
    search_columns = ["dttm", "dag_id", "task_id", "event", "execution_date", "owner", "extra"]
    label_columns = {
        "execution_date": "Logical Date",
    }
    base_order = ("dttm", "desc")
    base_filters = [["dag_id", DagFilter, lambda: []]]
    formatters_columns = {
        "dttm": wwwutils.datetime_f("dttm"),
        "execution_date": wwwutils.datetime_f("execution_date"),
        "dag_id": wwwutils.dag_link,
    }
class TaskRescheduleModelView(AirflowModelView):
    """View to show records from Task Reschedule table."""
    route_base = "/taskreschedule"
    datamodel = AirflowModelView.CustomSQLAInterface(models.TaskReschedule)  
    related_views = [DagRunModelView]
    class_permission_name = permissions.RESOURCE_TASK_RESCHEDULE
    method_permission_name = {
        "list": "read",
    }
    base_permissions = [
        permissions.ACTION_CAN_READ,