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.

("BT", "Bottom > Top"),
                ),
            )
        form = GraphForm(data=dt_nr_dr_data)
        form.execution_date.choices = dt_nr_dr_data["dr_choices"]
        task_instances = {}
        for ti in dag.get_task_instances(dttm, dttm):
            if ti.task_id not in task_instances:
                task_instances[ti.task_id] = wwwutils.get_instance_with_map(ti, session)
        tasks = {
            t.task_id: {
                "dag_id": t.dag_id,
                "task_type": t.task_type,
                "extra_links": t.extra_links,
                "is_mapped": isinstance(t, MappedOperator),
                "trigger_rule": t.trigger_rule,
            }
            for t in dag.tasks
        }
        if not tasks:
            flash("No tasks found", "error")
        session.commit()
        doc_md = wwwutils.wrapped_markdown(getattr(dag, "doc_md", None))
        task_log_reader = TaskLogReader()
        if task_log_reader.supports_external_link:
            external_log_name = task_log_reader.log_handler.log_name
        else:
            external_log_name = None
        state_priority = ["no_status" if p is None else p for p in wwwutils.priority]
        return self.render_template(