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.

form=form,
            root=root,
            dag=dag,
            title=title,
        )
    @expose("/xcom")
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_TASK_INSTANCE),
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_XCOM),
        ]
    )
    @action_logging
    @provide_session
    def xcom(self, session: Session = NEW_SESSION):
        """Retrieve XCOM."""
        dag_id = request.args["dag_id"]
        task_id = request.args.get("task_id")
        map_index = request.args.get("map_index", -1, type=int)
        
        
        execution_date = request.args.get("execution_date")
        dttm = _safe_parse_datetime(execution_date)
        form = DateTimeForm(data={"execution_date": dttm})
        root = request.args.get("root", "")
        dag = DagModel.get_dagmodel(dag_id)
        ti = session.query(TaskInstance).filter_by(dag_id=dag_id, task_id=task_id).first()
        if not ti:
            flash(f"Task [{dag_id}.{task_id}] doesn't seem to exist at the moment", "error")