Add support for P5 FutureNow light platform (#15662)

* Added support for FutureNow light platform and relay/dimmer units

* Pinned specific version for requirement

* Added support for FutureNow light platform and relay/dimmer units

* Added futurenow.py to .coveragerc.

* Minor fixes and enhancements as requested in the code review.

* Minor fixes and enhancements as requested in the code review.

* Use device_config's value directly as it's validated as boolean.

* Simplify state check.

* Fixed brightness update that was broken in previous commit.