Update auth token before sending it when the connection is established.

Current we send auth token to server whenever get/set (put/listen) request is queue, if the connection has been established.
It is not a very nice implementation and more changes will be made in b/123781317

This change would fix a bug if the event happens in the following order.
- Auth sign-in.
- auto db = Database::GetInstance(); (Create database, start connecting to server)
- db.GetReference().SetValue(1); (Put request added, and queue as pending request.  But no token sent because connection is not established yet)
- Connection established.  OnReady() called.  Since it does not retrieve auth_token_ at this point, no auth token would be sent to the server.
- Pending put requests sent before auth token message is sent => may result in permission deny.

PiperOrigin-RevId: 246432366

Author: chkuang-g

database/src/desktop/connection/persistent_connection.cc

@@ -187,6 +187,9 @@ void PersistentConnection::OnReady(int64_t timestamp,
   LogDebug("%s calling restore state", log_id_.c_str());
   assert(connection_state_ == kConnecting);
 
+  // Try to retrieve auth token synchronously when connection is ready.
+  GetAuthToken(&auth_token_);
+
   if (auth_token_.empty()) {
     LogDebug("%s Not restoring auth because token is null.", log_id_.c_str());
     connection_state_ = kConnected;