public PrometheusExpositionService build() {
        return new PrometheusExpositionService(prometheusRegistry,
                                               transientServiceOptionsBuilder.build());
    }
Returns a newly-created {@link PrometheusExpositionService} based on the properties
of this builder.
prometheus1/src/main/java/com/linecorp/armeria/server/prometheus/PrometheusExpositionServiceBuilder.java