chore(codegen): include default value comment for service id

Author: eduardomourar

codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/AddAwsRuntimeConfig.java

@@ -77,7 +77,10 @@ public void addConfigInterfaceFields(
             TypeScriptWriter writer
     ) {
         if (isAwsService(settings, model)) {
-            writer.writeDocs("Unique service identifier.\n@internal")
+            ServiceShape service = settings.getService(model);
+            String sdkId = service.getTrait(ServiceTrait.class).map(ServiceTrait::getSdkId)
+                    .orElse("");
+            writer.writeDocs(String.format("Unique service identifier.%n@internal%n@default \"%s\"", sdkId))
                     .write("serviceId?: string;\n");
         }
         if (isSigV4Service(settings, model)) {