private static Optional<ConfigInstance> getConfigFromModel(
            AbstractConfigProducerRoot configModel, Class<? extends ConfigInstance> configClass, String configKey) {
        try {
            return Optional.ofNullable(configModel.getConfig(configClass, configKey));
        } catch (Exception e) {
            return Optional.empty();
        }
    }
Returns the ConfigInstances classes from the annotation on the given Service class ,
including the ConfigInstances annotated on any of its super classes.
NOTE: Only the super classes that are subclass of Service are inspected.
config-model/src/main/java/com/yahoo/vespa/model/application/validation/change/ConfigValueChangeValidator.java