sendMessage method

Implementation

@override
Future<Message> sendMessage(String threadId, Message message) async {
  var url = 'https://api.openai.com/v1/threads/$threadId/messages';
  var response = await httpClient.post(
    url,
    data: message.toGptMap,
  );
  Map<String, dynamic> data = response.data;
  var newMessage = Message.fromMap(data);
  message.id = newMessage.id;
  return newMessage;
}