Add metrics exemplars to explore metrics page

[JamesNK]

Describe the issue or suggestion

There are docs that explore the metrics page. A new feature in 8.1 is metrics exemplars: https://learn.microsoft.com/en-us/dotnet/aspire/fundamentals/dashboard/explore#metrics-page

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Associated WorkItem - 292422

[IEvangelist]

Yes, OTEL - exemplars: https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exemplars