code: public void registerExtensions(final Class<?>... extensions) {
          for (Class<?> extension : extensions) {
              register(ConfigItem.Extension, extension);
          }
      }
docs: Usual extension registration from {@link ru.vyarus.dropwizard.guice.GuiceBundle.Builder#extensions(Class[])}
  or {@link ru.vyarus.dropwizard.guice.module.installer.bundle.GuiceyBootstrap#extensions(Class[])}.
  
  @param extensions extensions to register