FR: Prometheus Support

[snowzach]

It seems like it would be fairly trivial to add support for Prometheus. If you're not familiar, it requires an http endpoint and it exposes metrics in a really simple, human readable key/value format. It collects metrics by pulling data.

https://prometheus.io/docs/concepts/data_model/

I am thinking the easiest thing to expose would be a kwh counter or something like that and then gauges for everything else like freq and voltage. I am not sure how it's stored but a kwh counter would be nice vs say a guage which might miss a spike between readings. Not sure if it's possible to capture that info or not... Food for thought.

Suggestions:

iotawatt_power_current{device_name="<device_name>",input_name="<input_name"}=123  # Gauge value
iotawatt_power{device_name="<device_name>",input_name="<input_name"}=234234 # Counter value
iotawatt_voltage{device_name="<device_name>",phase?="<input_name"}=125.342 # Gauge value
iotawatt_frequency{device_name="<device_name>",phase?="<input_name"}=60.0 # Gauge value

[snowzach]

I opened PR #333 to add support.

[boblemaire]

Comment in PR.