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.

"""Shows task instances."""
        dag_id = request.args.get("dag_id")
        dag = get_airflow_app().dag_bag.get_dag(dag_id)
        dttm = request.args.get("execution_date")
        if dttm:
            dttm = _safe_parse_datetime(dttm)
        else:
            return {"error": f"Invalid execution_date {dttm}"}, 400
        with create_session() as session:
            task_instances = {
                ti.task_id: wwwutils.get_instance_with_map(ti, session)
                for ti in dag.get_task_instances(dttm, dttm)
            }
        return flask.json.jsonify(task_instances)
    @expose("/object/grid_data")
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
        ]
    )
    def grid_data(self):