* Fix MQTT Light with RGB and Brightness
When an MQTT light is given an RGB and Brightness topic, the RGB
is scaled by the brightness *as well* as the brightness being set
This causes 255,0,0 at 50% brightness to be sent as 127,0,0 at 50%
brightness, which ends up as 63,0,0 after the RGB bulb has applied
its brightness scaling.
Fixes the same issue in mqtt, mqtt-json and mqtt-template.
Related Issue: #13725
* Add comment to mqtt_json as well