Add support for KEYBOARD_BACKLIGHT to LightsManager API

Add new light type for KEYBOARD_BACKLIGHT to be used to
find if the Light is of type keyboard backlight
We will add code to modify Keyboard backlight based on key
events in future CLs

Test: None
Bug: 245506418
Change-Id: I0c7efb687c74c029e61c878c55f3af40710ec86d