Metrics API in azure-core and otel implementation

[lmolkova]

Fixes #25603 and #25604

Context: https://gist.github.com/lmolkova/b9004307a09be788af04f05ebe22ad3c

Introduces metrics API in azure-core and its implementation in azure-core-metrics-opentelemetry.
Micrometer-based implementation is included as a sample.

Micro-benchmarks: <100 ns per measurement (~30 of them in Instant.now()x2), no allocations

Benchmark                                                                 Mode  Cnt   Score   Error  Units
OpenTelemetryMetricsBenchmark.basicHistogram                              avgt    6  75.781 ±  4.055  ns/op
OpenTelemetryMetricsBenchmark.basicHistogramWithCommonAndExtraAttributes  avgt    6  92.401 ±  6.281  ns/op
OpenTelemetryMetricsBenchmark.basicHistogramWithCommonAttributes          avgt    6  85.797 ± 16.855  ns/op
OpenTelemetryMetricsBenchmark.disabledNotOptimizedMetrics                 avgt    6  30.738 ±  2.421  ns/op
OpenTelemetryMetricsBenchmark.disabledOptimizedMetrics                    avgt    6   0.460 ±  0.013  ns/op
OpenTelemetryMetricsBenchmark.noopMeterProviderNotOptimized               avgt    6  33.055 ±  2.987  ns/op

Perf-tests: EvenHubs producer test ~6% overhead, need more work to properly measure:

Completed 56,180 operations in a weighted-average of 305.26s (184.04 ops/s, 0.005 s/op) - metrics off
Completed 60,923 operations in a weighted-average of 307.40s (198.19 ops/s, 0.005 s/op) - metrics on

EventHubs advanced usage prototype (perf-tested above):

https://github.com/lmolkova/azure-sdk-for-java/blob/9bc8e11b420ca91ad8760283a064044e88781d3a/sdk/eventhubs/azure-messaging-eventhubs/src/main/java/com/azure/messaging/eventhubs/EventHubProducerAsyncClient.java#L601

https://github.com/lmolkova/azure-sdk-for-java/blob/metrics-api-proto/sdk/eventhubs/azure-messaging-eventhubs/src/main/java/com/azure/messaging/eventhubs/EventHubsMetricProducerMetricHelper.java

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-core

[srnagar]

LGTM

[stliu]

Thanks @lmolkova

@yiliuTo @saragluna FYI, now we are able to start the issue of enabling metrics in spring

[lmolkova]

@stliu @yiliuTo @saragluna let me know if you need any help! Note that SDKs don't emit metrics yet, we just have API to start doing it, but stay tuned for AMQP metrics coming - I hope to have the first AMQP metrics (from core) coming next month.