function createClientWithAppCredentials () {
  // For more information on app authentication, see
  // https://developers.google.com/workspace/chat/authenticate-authorize-chat-app
  return new ChatServiceClient({
    keyFile: SERVICE_ACCOUNT_FILE,
    scopes: APP_AUTH_OAUTH_SCOPES,
  });
}
Create a new Chat service client with application credentials.

@returns {ChatServiceClient} The resulting client for the Chat service