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.

)
        if conf.getboolean("webserver", "SHOW_RECENT_STATS_FOR_COMPLETED_RUNS", fallback=True):
            last_dag_run = (
                session.query(DagRun.dag_id, sqla.func.max(DagRun.execution_date).label("execution_date"))
                .join(DagModel, DagModel.dag_id == DagRun.dag_id)
                .filter(DagRun.state != State.RUNNING, DagModel.is_active)
                .group_by(DagRun.dag_id)
            )
            last_dag_run = last_dag_run.filter(DagRun.dag_id.in_(filter_dag_ids))
            last_dag_run = last_dag_run.subquery("last_dag_run")
            
            
            last_task_instance_query_result = (
                session.query(
                    TaskInstance.dag_id.label("dag_id"),
                    TaskInstance.state.label("state"),
                    sqla.literal(False).label("is_dag_running"),
                )
                .join(TaskInstance.dag_run)
                .join(
                    last_dag_run,
                    and_(
                        last_dag_run.c.dag_id == TaskInstance.dag_id,
                        last_dag_run.c.execution_date == DagRun.execution_date,
                    ),
                )
            )
            final_task_instance_query_result = union_all(
                last_task_instance_query_result, running_task_instance_query_result
            ).alias("final_ti")