Numeric error flag in MQTT

[CFlix]

The Feature

Currently the "error" value in the MQTT value(s) is a string. This is however unhandy to directly store e.g. in Influxdb and use in visualizations like Grafana.
I therefore propose to add a numeric error indicator that

• shall have a value of 0 if no error occurred in the reading
• shall have a value other than 0 if an error occurred
• may have different error indicating values other than 0 to indicate the error more precisely