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.

query = query.filter(DagRun.state == run_state)
            dag_runs = wwwutils.sorted_dag_runs(query, ordering=dag.timetable.run_ordering, limit=num_runs)
            encoded_runs = [
                wwwutils.encode_dag_run(dr, json_encoder=utils_json.WebEncoder) for dr in dag_runs
            ]
            data = {
                "groups": dag_to_grid(dag, dag_runs, session),
                "dag_runs": encoded_runs,
                "ordering": dag.timetable.run_ordering,
            }
        
        return (
            htmlsafe_json_dumps(data, separators=(",", ":"), dumps=flask.json.dumps),
            {"Content-Type": "application/json; charset=utf-8"},
        )
    @expose("/object/next_run_datasets/<string:dag_id>")
    @auth.has_access([(permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG)])
    def next_run_datasets(self, dag_id):
        """Returns datasets necessary, and their status, for the next dag run."""
        dag = get_airflow_app().dag_bag.get_dag(dag_id)
        if not dag:
            return {"error": f"can't find dag {dag_id}"}, 404
        with create_session() as session:
            data = [
                dict(info)
                for info in session.query(
                    DatasetModel.id,
                    DatasetModel.uri,
                    func.max(DatasetEvent.timestamp).label("lastUpdate"),
                )