private void renderGroupingGroupSyntheticFields(Hit hit) throws IOException {
        renderGroupMetadata(((Group) hit).getGroupId());
        if (hit instanceof RootGroup) {
            renderContinuations(Map.of(Continuation.THIS_PAGE, ((RootGroup) hit).continuation()));
        }
    }
Creates a json renderer using a custom executor.
Using a custom executor is useful for tests to avoid creating new threads for each renderer registry.
container-search/src/main/java/com/yahoo/search/rendering/JsonRenderer.java