unbanUser method
Unbans a user from this channel
Implementation
Future<void> unbanUser({required String userId}) async {
  if (userId.isEmpty) {
    throw InvalidParameterError();
  }
  await _sdk.api.send(ChannelUserUnbanRequest(
    targetId: userId,
    channelType: channelType,
    channelUrl: channelUrl,
  ));
}