docs: public boolean isExistingIndex(String index) throws IOException {
          logger.debug("is existing index [{}]", index);
          try {
              Response restResponse = lowLevelClient.performRequest("GET", "/" + index);
              logger.trace("get index metadata response: {}", asMap(restResponse));
              return true;
          } catch (ResponseException e) {
              if (e.getResponse().getStatusLine().getStatusCode() == 404) {
                  logger.debug("index [{}] does not exist", index);
                  return false;
              }
              throw e;
          }
      }