Called when the socket receives all the chats from WhatsappWeb's WebSocket. When this event is
fired, it is guaranteed that all metadata excluding messages will be present. To access this
data use Store.chats(). If you also need the messages to be loaded, please refer to
Listener.onChatMessagesSync(Chat, boolean). Particularly old chats may come later
through Listener.onChatMessagesSync(Chat, boolean).