@Override
            public MeterIdPrefix completeRequestPrefix(MeterRegistry registry, RequestLog log) {
                return function.apply(registry, log);
            }
Returns a {@link MeterIdPrefixFunction} which generates a {@link MeterIdPrefix} from the given
{@link MeterRegistry} and {@link RequestOnlyLog}.
Both {@link #activeRequestPrefix(MeterRegistry, RequestOnlyLog)}
and {@link #completeRequestPrefix(MeterRegistry, RequestLog)} will return the same {@link MeterIdPrefix}
for the same input.
core/src/main/java/com/linecorp/armeria/common/metric/MeterIdPrefixFunction.java