Update RPC metric descriptions to match semantic conventions

Co-authored-by: trask <[email protected]>

Author: Copilot

instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/semconv/rpc/RpcClientMetrics.java

@@ -40,7 +40,7 @@ private RpcClientMetrics(Meter meter) {
     DoubleHistogramBuilder durationBuilder =
         meter
             .histogramBuilder("rpc.client.duration")
-            .setDescription("The duration of an outbound RPC invocation.")
+            .setDescription("Measures the duration of outbound RPC.")
             .setUnit("ms");
     RpcMetricsAdvice.applyClientDurationAdvice(durationBuilder);
     clientDurationHistogram = durationBuilder.build();

instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/semconv/rpc/RpcServerMetrics.java

@@ -40,7 +40,7 @@ private RpcServerMetrics(Meter meter) {
     DoubleHistogramBuilder durationBuilder =
         meter
             .histogramBuilder("rpc.server.duration")
-            .setDescription("The duration of an inbound RPC invocation.")
+            .setDescription("Measures the duration of inbound RPC.")
             .setUnit("ms");
     RpcMetricsAdvice.applyServerDurationAdvice(durationBuilder);
     serverDurationHistogram = durationBuilder.build();