Implement low power mode api

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: All
• Core Version: latest git today
• Development Env: All
• Operating System: All

Problem Description

PR #6989 provides a low power usage reference example, and it has been merged. Per @d-a-v 's comment, it should be investigated how to unify the current experimental pseudo modes with the reference code in the example, and how to provide a consistent api to the users. Once that api is available, the example in #6989 should be migrated to make use of that api without changing the current behavior of the tests in that example sketch.

MCVE Sketch

See the example merged in #6989.