Consider replacing ShNode.reporting_sample_period_s with something else

[jessicamillar]

Deserves a design discusion.

sample_period_s for an ShNode (object getting read) / TelemetryName pair: period at which the actor/driver should send a telemetry to Scada.

The issue is, for an actor/driver that reports multiple things, there is not a single such. For example the power meter has this info per node measured/telemetry name pair (in ConfigList/SamplePeriodS for ElectricMeterComponents).

reporting_sample_period_s would be better named default_sample_period_s. Consider doing this and making it the default in scada code