Add GJ (gigajoule) as an energy meter unit (#2114)

Some district heating meters are displaying their values in GJ and Home
Assistant is also capable of accepting heating values in this format.

code/components/jomjol_flowcontroll/ClassFlowMQTT.cpp

@@ -156,6 +156,9 @@ bool ClassFlowMQTT::ReadParameter(FILE* pfile, string& aktparamgraph)
             else if (toUpper(splitted[1]) == "ENERGY_MWH") {
                 mqttServer_setMeterType("energy", "MWh", "h", "MW");
             }
+            else if (toUpper(splitted[1]) == "ENERGY_GJ") {
+                mqttServer_setMeterType("energy", "GJ", "h", "GJ/h");
+            }
         }
 
         if ((toUpper(splitted[0]) == "CLIENTID") && (splitted.size() > 1))

sd-card/html/edit_config_param.html

@@ -654,6 +654,7 @@ textarea {
 					<option value="energy_wh">Energymeter (Value: Wh, Rate: W)</option>
 					<option value="energy_kwh">Energymeter (Value: kWh, Rate: kW)</option>
 					<option value="energy_mwh">Energymeter (Value: MWh, Rate: MW)</option>
+					<option value="energy_gj">Energymeter (Value: GJ, Rate: GJ/h)</option>
 				</select>
 			</td>
 			<td>$TOOLTIP_MQTT_MeterType</td>