add SLEEP mode

[daggy72]

studying the manual of my remote and indoor unit I discovered the SLEEP button/function. This is what I have been looking for to activate in combination with certain scenes, like "OK Google - Goodnight" ;-)

[DomiStyle]

Just like with the power usage stats I'm currently not interested in reverse engineering any automation related features since I use Home Assistant to control my AC. Including turning them off when I sleep.

But I will leave the issue open in case anybody wants to take a look.