public RegistryClient.Factory newBaseImageRegistryClientFactory(String serverUrl) {
    return RegistryClient.factory(
            getEventHandlers(), serverUrl, baseImageConfiguration.getImageRepository(), httpClient)
        .setUserAgent(makeUserAgent());
  }
Creates a new {@link com.google.cloud.tools.jib.registry.RegistryClient.Factory} for the base
image repository on the registry {@code serverUrl}. Compared to @link
#newBaseImageRegistryClientFactory()), this method is useful to try a mirror.

@param serverUrl the server URL for the registry (for example, {@code gcr.io})
@return a new {@link com.google.cloud.tools.jib.registry.RegistryClient.Factory}
jib-core/src/main/java/com/google/cloud/tools/jib/configuration/BuildContext.java