ComplexKafkaPrincipal implementation to allow adding group information to user principals

ComplexKafkaPrincipal.java

public class ComplexKafkaPrincipal extends KafkaPrincipal{

  protected List<KafkaPrincipal> additionalPrincipals = new ArrayList<>();
  public ComplexKafkaPrincipal(String principalType, String name) {
      super(principalType, name);
  }

  public ComplexKafkaPrincipal(KafkaPrincipal kafkaPrincipal) {
      this(kafkaPrincipal.getPrincipalType(), kafkaPrincipal.getName());
  }

  public ComplexKafkaPrincipal(String principalType, String name, List<KafkaPrincipal> additionalPrincipals) {
      this(principalType, name);
      this.additionalPrincipals = additionalPrincipals;
  }

  public List<KafkaPrincipal> getGroupMemberships() {
      return additionalPrincipals;
  }
}