Provide a way to customize meters

[ikhoon]

One DistributionStatisticConfig is shared to configure both Timer and DistributionSummary.
This limitation prevents users from being able to customize Armeria meters with various options.
Users may want to configure different configurations for request.duration and request.length.

Proposal: Provide an API that creates a new Timer or DistributionSummary.

interface MeterFactory {
  Timer newTimer(MeterRegistry registry, String name, Iterable<Tag> tags);

  DistributionSummary newDistributionSummary(MeterRegistry registry,
                                             String name, Iterable<Tag> tags);

  ...
}

In addition to MetricCollecting{Service,Client}, meters are wildly used in Armeria internally, ServerBuilder and ClientFactoryBulder would be proper locations to set.

Server
  .builder()
  .meterFactory(myMeterFactory)

ClientFactory
  .builder()
  .meterFactory(myMeterFactory)

#5661 (comment)