private List<File> sortFiles(File dir) {
        ArrayList<File> files = new ArrayList<>();
        files.addAll(List.of(dir.listFiles()));
        Collections.sort(files);
        return files;
    }
Reads a single page template file.

@throws RuntimeException if <code>fileName</code> is not a readable file, or if there is some error in the XML
container-search/src/main/java/com/yahoo/search/pagetemplates/config/PageTemplateXMLReader.java