Remove SensorMetricSample in favour of MetricSample

This commit removes the `SensorMetricSample` message in favour of using
`MetricSample` for sensors. The `SensorMetricSample` message was
a subset of the `MetricSample` message.

From a design perspective focused on consistency, flexibility, and
minimizing API surface area while handling variations via optional
fields (which is idiomatic in Protobuf3), there's a strong argument that
`SensorMetricSample` is redundant and potentially confusing, and that
having only `MetricSample` is a cleaner design.

Signed-off-by: Tiyash Basu <[email protected]>

Author: tiyash-basu-frequenz

RELEASE_NOTES.md

@@ -35,6 +35,7 @@
 - Renamed `SensorState` to `SensorStateSnapshot` to better reflect its purpose.
 - Renamed `sampled_at` timestamps for state snapshots to `origin_time`.
 - Renamed `sampled_at` timestamps for metric samples to `sample_time`.
+- Remove `SensorMetricSample` in favour of using `MetricSample` for sensors.
 
 ## Bug Fixes
 

proto/frequenz/api/common/v1/microgrid/sensors/sensors.proto

@@ -233,11 +233,15 @@ message SensorMetricSample {
 //          sample_time: "2023-10-01T00:00:00Z",
 //          metric: "METRIC_SENSOR_TEMPERATURE",
 //          value: metric_value_variant: {simple_metric: {value: 23.5},
+//          bounds: {}
+//          source: {}
 //        },
 //        {
 //          sample_time: "2023-10-01T00:00:00Z",
 //          metric: "METRIC_SENSOR_RELATIVE_HUMIDITY",
 //          value: metric_value_variant: {simple_metric: {value: 23.5},
+//          bounds: {}
+//          source: "humidity_sensor_1"
 //        }
 //      ],
 //      states: [
@@ -254,7 +258,7 @@ message SensorData {
   uint64 sensor_id = 1;
 
   // List of measurements for a metric of the specific microgrid sensor.
-  repeated SensorMetricSample metric_samples = 2;
+  repeated frequenz.api.common.v1.metrics.MetricSample metric_samples = 2;
 
   // List of states of a specific microgrid sensor.
   repeated SensorStateSnapshot states = 3;