Improve eviction and expiration of labeled metrics

[devromik]

1. AbstractMeter: order MetricInstances within the same millisecond based on their insertion order.
2. Provide CompletableFuture<Iterator> iterator(Executor completionExecutor) to return iterator after removeExpiredInstances(). Update exporters accordingly.
3. Make periodic actualisation (removeExpiredInstancesAndSchedule) of MetricInstances optional.
4. Consider eliminating EXPIRED_INSTANCES_REMOVAL_ADDITIONAL_DELAY_MS in
   executor.schedule(
   this::removeExpiredInstancesAndSchedule,
   baseDelayMs + EXPIRED_INSTANCES_REMOVAL_ADDITIONAL_DELAY_MS, MILLISECONDS);

Consider min(baseDelayMs, 10000)