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 DAG runs as calendar."""
        def _convert_to_date(session, column):
            """Convert column to date."""
            if session.bind.dialect.name == "mssql":
                return column.cast(Date)
            else:
                return func.date(column)
        dag = get_airflow_app().dag_bag.get_dag(dag_id, session=session)
        dag_model = DagModel.get_dagmodel(dag_id, session=session)
        if not dag:
            flash(f'DAG "{dag_id}" seems to be missing from DagBag.', "error")
            return redirect(url_for("Airflow.index"))
        wwwutils.check_import_errors(dag.fileloc, session)
        wwwutils.check_dag_warnings(dag.dag_id, session)
        root = request.args.get("root")
        if root:
            dag = dag.partial_subset(task_ids_or_regex=root, include_downstream=False, include_upstream=True)
        dag_states = (
            session.query(
                (_convert_to_date(session, DagRun.execution_date)).label("date"),
                DagRun.state,
                func.max(DagRun.data_interval_start).label("data_interval_start"),
                func.max(DagRun.data_interval_end).label("data_interval_end"),
                func.count("*").label("count"),
            )
            .filter(DagRun.dag_id == dag.dag_id)