* Move to explicit enable of `ZMK_PM_SOFT_OFF` to turn
on the feature and use the behaviors, which matches
how other features work, and helps with split and
testing schemes.
Moved battery configuration to its own page to match the feature page.
Documented that external power is disabled when in sleep mode.
Clarified that the *_START configs apply on first boot, and any changes
after that are persisted.
