[New article]: Guidance for using Exemplars

### Proposed topic or title

Exemplars are a feature of OpenTelemetry to enable tagging metrics with the request that caused them

### Location in table of contents.

Diagnostics / Tracing & Metrics

### Reason for the article

Describe the new feature, and cover any gotcha's.

### Article abstract

- Intro to exemplars
- Use aspire dashboard for example / screenshots
- How to configure OTel to enable exemplars
- How to customize when exemplars are written
- Guidance for those creating telemetry to ensure that the metrics and traces will be correctly coordinated.

Info Sources
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https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/docs/metrics/exemplars/README.md
https://github.com/dotnet/runtime/pull/104455

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