@Nullable
  @VisibleForTesting
  String getUserAgent() {
    return userAgent;
  }
Check if the authorization allows using the specified repository can be mounted by the remote
registry as a source for blobs. More specifically, we can only check if the repository is not
disallowed.

@param repository repository in question
@return {@code true} if the repository appears to be mountable
jib-core/src/main/java/com/google/cloud/tools/jib/registry/RegistryClient.java