public static void writeConfig(final AppConfig appConfig, final OutputStream outputStream) throws IOException {
        Config config = new Config();
        config.setYamlAppConfig(appConfig);
        writeConfig(config, outputStream);
    }
Reads a YAML string that has already been through the drop wizard env var substitution.
stroom-config/stroom-config-app/src/main/java/stroom/config/app/StroomYamlUtil.java