[feat] System Brightness listener

[WorkNedoPrograMax]

Description (What is the problem)

Would be good to have a possibility to listen to system brightness change

Solution suggestion

Add a Stream<double> onSystemBrightnessChanged like the way we have it for the current brightness

[aaassseee]

Hi @WorkNedoPrograMax I am currently working on this feature on feature/change_system_brightness branch

[aaassseee]

Please wait for feature finish

[aaassseee]

@WorkNedoPrograMax this feature should be added in version 2.0.0+1