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.

self.datamodel.delete_all(items)
        self.update_redirect()
        return redirect(self.get_redirect())
    @provide_session
    def set_task_instance_state(self, tis, target_state, session: Session = NEW_SESSION):
        """Set task instance state."""
        try:
            count = len(tis)
            for ti in tis:
                ti.set_state(target_state, session)
            session.commit()
            flash(f"{count} task instances were set to '{target_state}'")
        except Exception:
            flash("Failed to set state", "error")
    @action("set_running", "Set state to 'running'", "", single=False)
    @action_has_dag_edit_access
    @action_logging
    def action_set_running(self, tis):
        """Set state to 'running'."""
        self.set_task_instance_state(tis, State.RUNNING)
        self.update_redirect()
        return redirect(self.get_redirect())
    @action("set_failed", "Set state to 'failed'", "", single=False)
    @action_has_dag_edit_access
    @action_logging
    def action_set_failed(self, tis):