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.

child_instances = [
                    item
                    for sublist in (child["instances"] for child in children if "instances" in child)
                    for item in sublist
                    if item and item["run_id"] == run_id
                ]
                children_start_dates = (item["start_date"] for item in child_instances)
                children_end_dates = (item["end_date"] for item in child_instances)
                children_states = {item["state"] for item in child_instances}
                
                
                
                mapped_states: MutableMapping[str, int] = collections.defaultdict(int)
                for mis in mapped_instances.values():
                    child_states = {mi.state for mi in mis}
                    state = next(s for s in wwwutils.priority if s in child_states)
                    value = state.value if state is not None else "no_status"
                    mapped_states[value] += 1
                group_state = next((state for state in wwwutils.priority if state in children_states), None)
                group_start_date = min(filter(None, children_start_dates), default=None)
                group_end_date = max(filter(None, children_end_dates), default=None)
                return {
                    "task_id": task_group.group_id,
                    "run_id": run_id,
                    "state": group_state,
                    "start_date": group_start_date,
                    "end_date": group_end_date,
                    "mapped_states": mapped_states,