fix(o11y): Fully implement metrics attributes according to requirements

This commit ensures that all required metrics attributes for Golden
Signals are fully implemented in sdk-platform-java.
Specifically:
- Always populate `rpc.response.status_code` for both gRPC and HTTP transports.
- Conditionally populate `http.response.status_code` only for HTTP transport.
- Add `error.type` attribute to metrics exclusively on operation failures.
- Ensured all other attributes (`gcp.client.service`, `rpc.system.name`, `rpc.method`, `url.domain`, `url.template`, `server.address`, `server.port`) are consistently populated from `ApiTracerContext.getMetricsAttributes()`.

Author: blakeli0

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/GoldenSignalsMetricsTracer.java

@@ -77,20 +77,23 @@ class GoldenSignalsMetricsTracer implements ApiTracer {
    */
   @Override
   public void operationSucceeded() {
-    attributes.put(RPC_RESPONSE_STATUS_ATTRIBUTE, StatusCode.Code.OK.toString());
+    ObservabilityUtils.populateStatusAttributes(attributes, null, transport);
     metricsRecorder.recordOperationLatency(
         clientRequestTimer.elapsed(TimeUnit.NANOSECONDS) / 1_000_000_000.0, attributes);
   }
 
   @Override
   public void operationCancelled() {
-    attributes.put(RPC_RESPONSE_STATUS_ATTRIBUTE, StatusCode.Code.CANCELLED.toString());
+    ObservabilityUtils.populateStatusAttributes(
+        attributes, new java.util.concurrent.CancellationException(), transport);
     metricsRecorder.recordOperationLatency(
         clientRequestTimer.elapsed(TimeUnit.NANOSECONDS) / 1_000_000_000.0, attributes);
   }
 
   @Override
   public void operationFailed(Throwable error) {
+    attributes.put(
+        ObservabilityAttributes.ERROR_TYPE_ATTRIBUTE, ObservabilityUtils.extractErrorType(error));
     ObservabilityUtils.populateStatusAttributes(attributes, error, transport);
     metricsRecorder.recordOperationLatency(
         clientRequestTimer.elapsed(TimeUnit.NANOSECONDS) / 1_000_000_000.0, attributes);

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/ObservabilityUtils.java

@@ -175,11 +175,10 @@ static void populateStatusAttributes(
       @Nullable Throwable error,
       ApiTracerContext.Transport transport) {
     StatusCode.Code code = extractStatus(error);
+    attributes.put(ObservabilityAttributes.RPC_RESPONSE_STATUS_ATTRIBUTE, code.toString());
     if (transport == ApiTracerContext.Transport.HTTP) {
       attributes.put(
           ObservabilityAttributes.HTTP_RESPONSE_STATUS_ATTRIBUTE, (long) code.getHttpStatusCode());
-    } else {
-      attributes.put(ObservabilityAttributes.RPC_RESPONSE_STATUS_ATTRIBUTE, code.toString());
     }
   }
 

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/tracing/GoldenSignalsMetricsTracerTest.java

@@ -163,6 +163,8 @@ void operationFailed_shouldRecordsOKStatus() {
     assertThat(metricData.getHistogramData().getPoints().iterator().next().getAttributes())
         .isEqualTo(
             Attributes.of(
+                AttributeKey.stringKey(ObservabilityAttributes.ERROR_TYPE_ATTRIBUTE),
+                "INTERNAL",
                 AttributeKey.stringKey(RPC_RESPONSE_STATUS_ATTRIBUTE),
                 StatusCode.Code.INTERNAL.toString()));
   }