addToContacts method
Adds the user to the contacts list of the authenticated MyUser.
Only meaningful, if this chat is a dialog.
Implementation
Future<void> addToContacts() async {
  if (_contactId == null) {
    try {
      await _contactService.createChatContact(user!.user.value);
    } catch (e) {
      MessagePopup.error(e);
      rethrow;
    }
  }
}