Add power availability tracking

[rthinman]

There is a skeleton in place in business_logic/src/aggregator.rs and business_logic/src/power_availability.rs.

Will need to update those files as well as logger.rs and main.rs.

Features:

• track seconds of power on each sample and each aggregation period
• track power alarms (power off for more than 24 hours). This is a feature that stationary logger C code did not implement.