code: public T payload(Resource payloadResource, Charset charset) {
          try {
              setPayload(FileUtils.readToString(payloadResource, charset));
          } catch (IOException e) {
              throw new CitrusRuntimeException("Failed to read payload resource", e);
          }
  
          return self;
      }
docs: Expect this message payload data in received message.
  @param payloadResource
  @param charset
  @return