code: public ResponseBuilder addHintDirective(String hintText) {
          PlainTextHint hint = PlainTextHint.builder()
                  .withText(hintText)
                  .build();
          HintDirective hintDirective = HintDirective.builder()
                  .withHint(hint)
                  .build();
          return addDirective(hintDirective);
      }
docs: Adds a {@link HintDirective} to the response.
  
  @param hintText hint text
  @return response builder