fix(rpc): propagate serviceName to ApiTracerContext when creating TracerFactory

Author: blakeli0

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/rpc/ClientContext.java

@@ -311,6 +311,7 @@ static ApiTracerFactory getApiTracerFactory(
           ApiTracerContext.newBuilder()
               .setServerAddress(endpointContext.resolvedServerAddress())
               .setServerPort(endpointContext.resolvedServerPort())
+              .setServiceName(endpointContext.serviceName())
               .setLibraryMetadata(settings.getLibraryMetadata())
               .build();
       apiTracerFactory = apiTracerFactory.withContext(apiTracerContext);