public static DockerConfigCredentialRetriever createForLegacyFormat(
      String registry, Path dockerConfigFile) {
    return new DockerConfigCredentialRetriever(registry, dockerConfigFile, true);
  }
Retrieves registry credentials from the Docker config.

<p>The credentials are searched in the following order (stopping when credentials are found):

<ol>
  <li>The credential helper from {@code credHelpers} defined for a registry, if available.
  <li>The {@code credsStore} credential helper, if available.
  <li>If there is an {@code auth} defined for a registry.
</ol>

@see <a
    href="https://docs.docker.com/engine/reference/commandline/login/">https://docs.docker.com/engine/reference/commandline/login/</a>
jib-core/src/main/java/com/google/cloud/tools/jib/registry/credentials/DockerConfigCredentialRetriever.java