Add display brightness slider to nightlight indicator controls, too

### Problem

The night light indicator wing panel icon looks very similar to the brightness symbol in the battery indicator wingpanel menu
This often leads users to the wrong place when they want to adjust the display brightness on their laptop.

### Proposal

Add the same brightness control to the night light wingpanel menu like the one that already exists on the battery indicator menu.
I'd suggest keeping the control on both menus though so that users who are used to find it on the battery menu will still find it, too.

### Prior Art (Optional)

_No response_