private List<Path> getDockerFiles(Path configDir) {
    return Arrays.asList(
        configDir.resolve(DOCKER_CONFIG_FILE),
        configDir.resolve(KUBERNETES_DOCKER_CONFIG_FILE),
        configDir.resolve(LEGACY_DOCKER_CONFIG_FILE));
  }
Makes a list of {@link CredentialRetriever}s.

@return the list of {@link CredentialRetriever}s
@throws FileNotFoundException if a credential helper path is specified, but the file doesn't
    exist
jib-plugins-common/src/main/java/com/google/cloud/tools/jib/plugins/common/DefaultCredentialRetrievers.java