[Feature] [Battery/Display] DDC/CI support for adjusting external monitor brightness

[joewood9364]

https://github.com/davidhi7/ddcci-plasmoid
The above KDE plasmoid allows users to change external monitor brightness which is very useful but also not very easy to install and does not integrate into KDE's native brightness adjustment sliders.

Ideally brightness adjustment of monitors would be a native feature akin to laptop screen brightness adjustment - COSMIC having this functionality by default would be a welcome improvement over competing DEs.