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.

)
                    record["end_date"] = max(
                        filter(None, [record["end_date"], ti_summary.end_date]), default=None
                    )
                    record["mapped_states"][ti_summary.state] = ti_summary.state_count
                if record:
                    set_overall_state(record)
                    yield record
            if isinstance(item, MappedOperator) or is_parent_mapped:
                instances = list(_mapped_summary(grouped_tis.get(item.task_id, [])))
            else:
                instances = list(map(_get_summary, grouped_tis.get(item.task_id, [])))
            return {
                "id": item.task_id,
                "instances": instances,
                "label": item.label,
                "extra_links": item.extra_links,
                "is_mapped": isinstance(item, MappedOperator) or is_parent_mapped,
                "has_outlet_datasets": any(isinstance(i, Dataset) for i in (item.outlets or [])),
                "operator": item.operator_name,
                "trigger_rule": item.trigger_rule,
            }
        
        task_group = item
        group_is_mapped = isinstance(task_group, MappedTaskGroup)
        children = [
            task_group_to_grid(child, grouped_tis, is_parent_mapped=group_is_mapped)
            for child in task_group.topological_sort()
        ]
        def get_summary(dag_run: DagRun):