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.

"""Set state to running."""
        return self._set_dag_runs_to_active_state(drs, State.RUNNING)
    @provide_session
    def _set_dag_runs_to_active_state(self, drs: list[DagRun], state: str, session: Session = NEW_SESSION):
        """This routine only supports Running and Queued state."""
        try:
            count = 0
            for dr in session.query(DagRun).filter(DagRun.id.in_([dagrun.id for dagrun in drs])):
                count += 1
                if state == State.RUNNING:
                    dr.start_date = timezone.utcnow()
                dr.state = state
            session.commit()
            flash(f"{count} dag runs were set to {state}.")
        except Exception as ex:
            flash(str(ex), "error")
            flash("Failed to set state", "error")
        return redirect(self.get_default_url())
    @action(
        "set_failed",
        "Set state to 'failed'",
        "All running task instances would also be marked as failed, are you sure?",
        single=False,
    )
    @action_has_dag_edit_access
    @provide_session
    @action_logging
    def action_set_failed(self, drs: list[DagRun], session: Session = NEW_SESSION):