Rinnai Gas Heater (FTR557) node

[brendanl]

Opto isolated from existing Rinnai controls and feedback.

All documented at https://techconz.com/smart-home/rinnai-gas-heater-ftr557/

Still to establish some OpenHAB rules for it, but will likely be Mon-Fri @ 7am when < 11 degrees outside, turn on.