public ClientDecorationBuilder add(Function<? super HttpClient, ? extends HttpClient> decorator) {
        decorators.add(requireNonNull(decorator, "decorator"));
        return this;
    }
Adds the specified HTTP-level {@code decorator}.

@param decorator the {@link Function} that transforms an {@link HttpClient} to another
core/src/main/java/com/linecorp/armeria/client/ClientDecorationBuilder.java