SMETS2 gas meter consumption is measured in m3 rather than kWh, so conversion from one unit to the other is required. Algorithm and description of terms is taken from: https://www.theenergyshop.com/guides/how-to-convert-gas-units-to-kwh This commit adds additional config file options to the `gas` section: - `meter_type` (default `1` for backward compatibility) Enables unit conversion from m3 to kWh before reporting metrics to influxdb - `volume_correction_factor` (default `1.02264`) - `calorific_value` (default `40`)