final <X extends AmazonWebServiceRequest> X appendUserAgent(
            X request, String userAgent) {
            request.getRequestClientOptions().appendUserAgent(userAgent);
            return request;
        }
Appends a user agent to the request's USER_AGENT_V1 client marker.
This method is intended only for internal use by the Amazon Web Services SDK.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/AmazonS3EncryptionClient.java