message: [dbus] refine DBus `GetProperty` error logs
  This commit refines DBus GetProperty error logs:
  Use INFO log level if the property is valid but handler returns
  error (used to be WARN)
diff: @@ -135,6 +135,7 @@ void DBusObject::GetPropertyMethodHandler(DBusRequest &aRequest)
  std::string interfaceName;
  std::string propertyName;
  otError error = OT_ERROR_NONE;
  + otError replyError = OT_ERROR_NONE;
  VerifyOrExit(reply != nullptr, error = OT_ERROR_NO_BUFS);
  VerifyOrExit(dbus_message_iter_init(aRequest.GetMessage(), &iter), error = OT_ERROR_FAILED);
  @@ -152,11 +153,11 @@ void DBusObject::GetPropertyMethodHandler(DBusRequest &aRequest)
  VerifyOrExit(interfaceIter != interfaceHandlers.end(), error = OT_ERROR_NOT_FOUND);
  dbus_message_iter_init_append(reply.get(), &replyIter);
  - SuccessOrExit(error = interfaceIter->second(replyIter));
  + SuccessOrExit(replyError = interfaceIter->second(replyIter));
  }
  }
  exit:
  - if (error == OT_ERROR_NONE)
  + if (error == OT_ERROR_NONE && replyError == OT_ERROR_NONE)
  {
  if (otbrLogGetLevel() >= OTBR_LOG_DEBUG)
  {
  @@ -166,6 +167,12 @@ exit:
  dbus_connection_send(aRequest.GetConnection(), reply.get(), nullptr);
  }
  + else if (error == OT_ERROR_NONE)
  + {
  + otbrLogInfo("GetProperty %s.%s reply:%s", interfaceName.c_str(), propertyName.c_str(),
  + ConvertToDBusErrorName(replyError));
  + aRequest.ReplyOtResult(replyError);
  + }
  else
  {
  otbrLogWarning("GetProperty %s.%s error:%s", interfaceName.c_str(), propertyName.c_str(),
  