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.

"start_date": (dag.start_date or now).date().isoformat(),
            "end_date": (dag.end_date or now).date().isoformat(),
        }
        return self.render_template(
            "airflow/calendar.html",
            dag=dag,
            doc_md=wwwutils.wrapped_markdown(getattr(dag, "doc_md", None)),
            data=htmlsafe_json_dumps(data, separators=(",", ":")),  
            root=root,
            dag_model=dag_model,
        )
    @expose("/graph")
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_LOG),
        ]
    )
    @gzipped
    @action_logging
    def legacy_graph(self):
        """Redirect from url param."""
        return redirect(url_for("Airflow.graph", **sanitize_args(request.args)))
    @expose("/dags/<string:dag_id>/graph")
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_LOG),