code: public MetricName withTag(String key, String value) {
  		return name(name).tags(tags).tag(key, value).build();
  	}
docs: Returns a copy of this name and appends a single tag
  <p>
  Note that this method does not override existing tags
  
  @param key   the key of the tag
  @param value the value of the tag
  @return a copy of this name including the provided tag