Set<String> getAdditionalTags() {
    return ImmutableSet.copyOf(additionalTags);
  }
Adds mirrors for a base image registry. Jib will try its mirrors in the given order before
finally trying the registry.

@param registry base image registry for which mirrors are configured
@param mirrors a list of mirrors, where each element is in the form of {@code host[:port]}
@return this
jib-core/src/main/java/com/google/cloud/tools/jib/api/Containerizer.java