Path getCredentialHelper() {
    return credentialHelper;
  }
Calls the credential helper CLI.

<p>Calls occur in the form:

<pre>{@code
echo -n <server URL> | docker-credential-<credential helper suffix> get
}</pre>

@return the Docker credentials by calling the corresponding CLI
@throws IOException if writing/reading process input/output fails
@throws CredentialHelperUnhandledServerUrlException if no credentials could be found for the
    corresponding server
@throws CredentialHelperNotFoundException if the credential helper CLI doesn't exist
jib-core/src/main/java/com/google/cloud/tools/jib/registry/credentials/DockerCredentialHelper.java