message: config: use ProtobufWkt when referencing well-known types.
diff: @@ -229,7 +229,7 @@ RouteEntryImplBase::parseOpaqueConfig(const envoy::api::v2::Route& route) {
  return ret;
  }
  for (auto it : filter_metadata->second.fields()) {
  - if (it.second.kind_case() == Protobuf::Value::kStringValue) {
  + if (it.second.kind_case() == ProtobufWkt::Value::kStringValue) {
  ret.emplace(it.first, it.second.string_value());
  }
  }
  