First draft of a doc for Tracing in networking

[samsp-msft]

Summary

Adds a new page for Tracing as part of Networking.

Work to be done:

• [ ] Needs TOC changes
• [ ] Needs a page listing the trace sources for networking (and other libraries)
• [x] We probably need to simplify the corresponding page for Metrics to use Aspire and link out for graphana usage

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Internal previews

📄 File	🔗 Preview link
docs/fundamentals/networking/telemetry/metrics.md	docs/fundamentals/networking/telemetry/metrics
docs/fundamentals/networking/telemetry/tracing.md	docs/fundamentals/networking/telemetry/tracing

[samsp-msft]

@antonfirsov - how are you doing with a reference page for the new spans?

[antonfirsov]

Closing in favor of #44063.