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.

conf=request_conf,
                form=form,
                is_dag_run_conf_overrides_params=is_dag_run_conf_overrides_params,
            )
        flash(f"Triggered {dag_id}, it should start any moment now.")
        return redirect(origin)
    def _clear_dag_tis(
        self,
        dag: DAG,
        start_date: datetime.datetime | None,
        end_date: datetime.datetime | None,
        *,
        origin: str | None,
        task_ids: Collection[str | tuple[str, int]] | None = None,
        recursive: bool = False,
        confirmed: bool = False,
        only_failed: bool = False,
        session: Session,
    ):
        if confirmed:
            count = dag.clear(
                start_date=start_date,
                end_date=end_date,
                task_ids=task_ids,
                include_subdags=recursive,
                include_parentdag=recursive,
                only_failed=only_failed,
                session=session,
            )
            msg = f"{count} task instances have been cleared"