cant update brightness slider without triggering fake brightness

[JarbasAl]

https://github.com/OpenVoiceOS/ovos-shell/blob/master/application/qml/panel/quicksettings/BrightnessSlider.qml#L28

if using a PHAL plugin to control the screen brightness, we want to update the slider position but NOT trigger fake brightness changes

related https://github.com/OpenVoiceOS/ovos-gui-plugin-shell-companion/pull/31

[JarbasAl]

i guess we need a config setting handled somewhere around here https://github.com/OpenVoiceOS/ovos-shell/blob/master/application/qml/main.qml#L336