subscribe method
This method subscribes the user to receiving notifications from a customer request.
Permissions required: Permission to view the customer request.
Implementation
Future<void> subscribe(String issueIdOrKey) async {
  await _client.send(
    'put',
    'rest/servicedeskapi/request/{issueIdOrKey}/notification',
    pathParameters: {
      'issueIdOrKey': issueIdOrKey,
    },
  );
}