public static List<Content> getContent(ConfigModelRepo pc) {
        List<Content> contents = new ArrayList<>();
        for (ConfigModel model : pc.asMap().values())
            if (model instanceof Content content)
                contents.add(content);
        return contents;
    }
Returns indexing cluster implicitly created by this,
or empty if an explicit cluster is used (or if called before the build phase)
config-model/src/main/java/com/yahoo/vespa/model/content/Content.java