@UnstableApi
    public static ArmeriaRetrofitBuilder builder(HttpPreprocessor httpPreprocessor) {
        return builder(WebClient.of(httpPreprocessor));
    }
Returns a new {@link ArmeriaRetrofitBuilder} which is configured with specified
{@link HttpPreprocessor}.
retrofit2/src/main/java/com/linecorp/armeria/client/retrofit2/ArmeriaRetrofit.java