fixup! Implement ReceiveComponentDataStream method

Fix issue loading optional fields

Author: llucax

src/frequenz/client/microgrid/metrics/_sample_proto.py

@@ -26,8 +26,8 @@ def aggregated_metric_sample_from_proto(
     """
     return AggregatedMetricValue(
         avg=message.avg_value,
-        min=message.min_value,
-        max=message.max_value,
+        min=message.min_value if message.HasField("min_value") else None,
+        max=message.max_value if message.HasField("max_value") else None,
         raw_values=message.raw_values,
     )