code: @Override
      public <R> CouchbaseManifestComparator<R> withKey(String key) {
          return new CouchbaseManifestComparator<>(
                                                   key, connection);
      }
docs: Create a new ManifestComparator with the same distributed map connection
  that targets a different key
  
  @param key
  Key to store data with
  @return new ManifestComparator that targets specified key