feat: add support for variable sleep durations

[pimlie]

This PR adds support to configure different sleep durations per day-of-week, hour and minute. It should basically support the most common configs as is described in hass.md, so instead of using home-assistant to keep changing the sleep duration it's just baked into the homeplate fw :)

• see config_example.cpp for example config
• I had to change the env's a little bit to be able to run the unit tests

[lanrat]

Thanks for the new feature! I left a few very minor nits.

[lanrat]

Thanks for the PR and new feature!

[felixh10r]

@pimlie @lanrat a quick heads-up because it took me a minute to find the problem: in config_example.h, sleep_duration.h was renamed to sleep_schedule.h but the file wasn't renamed. this line should be reverted, otherwise the correct file can't be found on build (i thought it's more elegant to amend the commit then to open a new PR—if i should, just say the word!)

[pimlie]

@felixh10r Ah damn, sorry about that. It is probably easiest/best to create a new PR to fix that, feel free to do so!