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.

"""Get Graph Data."""
        dag_id = request.args.get("dag_id")
        dag = get_airflow_app().dag_bag.get_dag(dag_id, session=session)
        root = request.args.get("root")
        if root:
            filter_upstream = request.args.get("filter_upstream") == "true"
            filter_downstream = request.args.get("filter_downstream") == "true"
            dag = dag.partial_subset(
                task_ids_or_regex=root, include_upstream=filter_upstream, include_downstream=filter_downstream
            )
        nodes = task_group_to_dict(dag.task_group)
        edges = dag_edges(dag)
        data = {
            "arrange": dag.orientation,
            "nodes": nodes,
            "edges": edges,
        }
        return (
            htmlsafe_json_dumps(data, separators=(",", ":"), dumps=flask.json.dumps),
            {"Content-Type": "application/json; charset=utf-8"},
        )
    @expose("/object/task_instances")
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
        ]
    )
    @action_logging
    def task_instances(self):