Implement the BATTERY_LIFE pulled atom.

Implement it alongside other pulled atoms surfacing data from health
HAL. The calculation estimates battery life using the battery-reported
full capacity and current, scaling to report in minutes and discard 4%
as an estimate for early shutdown before the battery fully discharges.

Flag: EXEMPT statsd atoms/metrics changes
Bug: 419415594
Test: statsd_testdrive 10245
Change-Id: If2d6bcbd5829fa37ac43b1c732e3399d45c8b623