message: fallback to route entry cluster name
diff: @@ -1194,7 +1194,11 @@ WasmResult Context::getProperty(absl::string_view path, std::string* result) {
  value = CelValue::CreateMessage(plugin_->listener_metadata_, &arena);
  break;
  case PropertyToken::CLUSTER_NAME:
  + if (!info->upstreamHost()->cluster().name().empty()) {
  value = CelValue::CreateString(&info->upstreamHost()->cluster().name());
  + } else {
  + value = CelValue::CreateString(&info->routeEntry()->clusterName());
  + }
  break;
  case PropertyToken::CLUSTER_METADATA:
  value = CelValue::CreateMessage(&info->upstreamHost()->cluster().metadata(), &arena);
  