public Containerizer withAdditionalTag(String tag) {
    Preconditions.checkArgument(ImageReference.isValidTag(tag), "invalid tag '%s'", tag);
    additionalTags.add(tag);
    return this;
  }
Adds an additional tag to tag the target image with. For example, the following would
containerize to both {@code gcr.io/my-project/my-image:tag} and {@code
gcr.io/my-project/my-image:tag2}:

<pre>{@code
Containerizer.to(RegistryImage.named("gcr.io/my-project/my-image:tag")).withAdditionalTag("tag2");
}</pre>

@param tag the additional tag to push to
@return this
jib-core/src/main/java/com/google/cloud/tools/jib/api/Containerizer.java