code: public Metadata add(String path, String value) {
          this.values.add(this.pathToProperty(path), value);
          this.addOp("add", path, value);
          return this;
      }
docs: Adds a new metadata value.
  @param path the path that designates the key. Must be prefixed with a "/".
  @param value the value.
  @return this metadata object.