Drop time-of-day tag which makes data difficult to use with victoria-metrics/promql

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`)

app/octopus_to_influxdb.py

@@ -102,7 +102,7 @@ def store_series(connection, series, metrics, rate_data):
         time = period.datetime().strftime('%H:%M')
         return {
             'active_rate': active_rate_field(measurement),
-            'time_of_day': time,
+            #'time_of_day': time,
         }
 
     measurements = [