startChatRoom method
Implementation
Future<String> startChatRoom(ChatMessage message, ChatRoom chatRoom) async {
final ref = _firestore.collection('ChatRooms').doc(
mergeStrings(senderMember?.userId ?? "", receiverMember?.userId ?? ""));
await ref.set(chatRoom.toJson());
final roomId = ref.id;
await sendMessage(message, roomId);
return roomId;
}