public <BUILDER extends ConfigInstance.Builder> BUILDER getConfig(BUILDER builder, String configId) {
        return (BUILDER) model.getConfig(builder, configId);
    }
Ask model to populate builder with config for a given config id. This method gives the same config as the
configserver would return to its clients.
@param builder The builder to populate
@param configId The config id of the producer to ask for config.
@return the same builder.
config-model/src/main/java/com/yahoo/config/model/test/TestRoot.java