public static Function<? super HttpClient, ObservationClient> newDecorator(
            ObservationRegistry observationRegistry,
            ObservationConvention<ClientObservationContext> observationConvention) {
        requireNonNull(observationRegistry, "observationRegistry");
        requireNonNull(observationConvention, "observationConvention");
        return delegate -> new ObservationClient(delegate, observationRegistry,
                                                 observationConvention);
    }
Creates a new micrometer observation integrated {@link HttpClient} decorator
using the specified {@link ObservationRegistry} and {@link ObservationConvention}.
core/src/main/java/com/linecorp/armeria/client/observation/ObservationClient.java