Add production_readingtime and consumption_readingtime output parameters

[lnlp]

Enhancement Request

Please add the following two output parameters:

• production_readingtime

• consumption_readingtime

Reporting of reading time for production and consumption is similar to the currently implemented reporting of inverter data, which includes the reading time for each inverter.
For the inverters reading time is output as array value without using a parameter name for the value.
The production and consumption related parameters each have their own named parameters, so it is probably best to create separate output parameters for the reading times.
Output format of production_readingtime and consumption_readingtime should be the same as that used for the inverter data.

This enhancement will work with newer Envoy models that output production.json.

consumption_readingtime should be output only when CT metering for Consumption is enabled.

When CT metering for Production is disabled readingTime should be taken from the production/inverters section in production.json. When CT metering for production is enabled readingTime should be taken from the production/eim section.

For additional information see issue #37.