code: public EventBuilder withTag(String tagKey, String tagValue) {
          event.getTags().put(tagKey, tagValue);
          return this;
      }
docs: Adds a tag to an event.
  <p>
  This allows to set a tag value in different contexts.
  
  @param tagKey   name of the tag.
  @param tagValue value of the tag.
  @return the current {@code EventBuilder} for chained calls.