code: public static void addCustomTagToState(State state, List<? extends Tag<?>> tags) {
      for (Tag<?> tag : tags) {
        state.appendToListProp(METRICS_STATE_CUSTOM_TAGS, tag.toString());
      }
    }
docs: Add a {@link List} of {@link Tag}s to a {@link org.apache.gobblin.configuration.State} with key {@link #METRICS_STATE_CUSTOM_TAGS}.
  
  <p>
  {@link org.apache.gobblin.metrics.Tag}s under this key can later be parsed using the method {@link #getCustomTagsFromState}.
  </p>
  
  @param state {@link org.apache.gobblin.configuration.State} state to add the tag to.
  @param tags list of {@link Tag}s to add.