code: public static Function<HttpRequest, String> PREFIXED_REQUEST_TARGET_NAME(final String prefix) {
      return (request) -> replaceIfNull(prefix, "")
          + replaceIfNull(standardizeUri(request.getRequestLine().getUri()), "unknown");
    }
docs: A configurable version of REQUEST_TARGET_NAME
  
  @param prefix The String prefix that will be appended to the name generated by the Function.
  @return A Function that, when given an HttpRequest, will return a String concatenation of the
  prefix and the Elasticsearch target of the request.