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.

"""Scheduled slots rendering."""
        pool_id = self.get("pool")
        scheduled_slots = self.get("scheduled_slots")
        if pool_id is not None and scheduled_slots is not None:
            url = url_for("TaskInstanceModelView.list", _flt_3_pool=pool_id, _flt_3_state="scheduled")
            return Markup("<a href='{url}'>{scheduled_slots}</a>").format(
                url=url, scheduled_slots=scheduled_slots
            )
        else:
            return Markup('<span class="label label-danger">Invalid</span>')
    formatters_columns = {
        "pool": pool_link,
        "running_slots": frunning_slots,
        "queued_slots": fqueued_slots,
        "scheduled_slots": fscheduled_slots,
    }
    validators_columns = {"pool": [validators.DataRequired()], "slots": [validators.NumberRange(min=-1)]}
def _can_create_variable() -> bool:
    return get_airflow_app().appbuilder.sm.has_access(
        permissions.ACTION_CAN_CREATE, permissions.RESOURCE_VARIABLE
    )
class VariableModelView(AirflowModelView):