nixos/release-notes: add power.ups entry

nixos/doc/manual/release-notes/rl-2411.section.md

@@ -565,6 +565,10 @@
 
 - `restic` module now has an option for inhibiting system sleep while backups are running, defaulting to off (not inhibiting sleep), available as [`services.restic.backups.<name>.inhibitsSleep`](#opt-services.restic.backups._name_.inhibitsSleep).
 
+- `power.ups` now powers off UPSs during a power outage event.
+  This saves UPS battery and ensures that host(s) get back up again when power comes back, even in the scenario when the UPS would have had enough capacity to keep power on during the whole power outage.
+  If you like the old behaviour of keeping the UPS on (and emptying the battery) after the hosts have shut down, and risk not getting a power cycle event to get the host back up, set `power.ups.upsmon.settings.POWERDOWNFLAG = null;`.
+
 - Support for *runner registration tokens* has been [deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/380872)
   in `gitlab-runner` 15.6 and is expected to be removed in `gitlab-runner` 18.0. Configuration of existing runners
   should be changed to using *runner authentication tokens* by configuring