Add transition for switch to night mode

[paviro]

There already is an option for a transition on daytime switch it would be really nice to also have one for switching to night mode. For example I have twi scenes with different bulbs being on + https://github.com/basnijholt/adaptive-lighting/ for changing the brightness / color temp. Right now enabling night mode changes my lights brightness and color temp. It would be great if the scene would also gets switched so only the correct lights are on.