Add metrics variants for inverter temperatures (#188)

Author: tiyash-basu-frequenz

RELEASE_NOTES.md

@@ -14,6 +14,11 @@
   the source of the metric, in case different sensors in component report
   metrics with the same `Metric` variant.
 
+- Added 3 new metric variants for inverter temperatures:
+  - `METRIC_INVERTER_TEMPERATURE_CABINET`
+  - `METRIC_INVERTER_TEMPERATURE_HEATSINK`
+  - `METRIC_INVERTER_TEMPERATURE_TRANSFORMER`
+
 ## Bug Fixes
 
 <!-- Here goes notable bug fixes that are worth a special mention or explanation -->

proto/frequenz/api/common/v1/metrics/metric_sample.proto

@@ -138,6 +138,9 @@ enum Metric {
 
   // General inverter metrics.
   METRIC_INVERTER_TEMPERATURE = 120;
+  METRIC_INVERTER_TEMPERATURE_CABINET = 121;
+  METRIC_INVERTER_TEMPERATURE_HEATSINK = 122;
+  METRIC_INVERTER_TEMPERATURE_TRANSFORMER = 123;
 
   // EV charging station metrics.
   METRIC_EV_CHARGER_TEMPERATURE = 140;