nut: Enable Podman auto-update for containers

Setting `AutoUpdate=registry` will tell Podman to automatically fetch
an updated container image from its corresponding registry and restart
the container.  The `podman-auto-update.timer` systemd unit needs to be
active for this to happen on a schedule.

templates/nut/nut-monitor.container

@@ -8,6 +8,7 @@ After=nut-server.service
 [Container]
 Image=git.pyrocufflink.net/containerimages/nut:latest
 Pull=newer
+AutoUpdate=registry
 Exec=upsmon -F
 User=nut
 RunInit=true

templates/nut/nut-server.container

@@ -10,6 +10,7 @@ After=reload-udev-rules.path
 [Container]
 Image=git.pyrocufflink.net/containerimages/nut:latest
 Pull=newer
+AutoUpdate=registry
 RunInit=true
 Volume=%t/containers/udev-rules:/etc/udev/rules.d:rw,z
 Volume=/etc/ups:/etc/ups:ro