public Optional<String> getCredentialHelper() {
    if (credentials != null && credentials.credentialHelper != null) {
      return Optional.of(credentials.credentialHelper);
    }
    return Optional.empty();
  }
Returns the user configured credential helper for any registry during the build, this can be
interpreted as a path or a string.

@return a Optional string reference to the credential helper
jib-cli/src/main/java/com/google/cloud/tools/jib/cli/CommonCliOptions.java