Distributed tracing in networking

[antonfirsov]

This is a major rework of #42830, extending the content, making the information more specific and IMO easier to follow. The biggest change is the in the collection paragraphs:

• I dropped the definitions of terms instrumentation, collection, export, OpenTelemetry etc., given that we were already using them in the intro, so it felt rather pointless to define them at that point; IMO the reader is looking for practical guidelines and examples anyways.
• Instead, I added a summary of the available methods, so readers can navigate the document following their preferences and goals.
• Metrics.md: Added back the dotnet-monitor example. Reintroduced a short paragraph on prometheus/grafana, since the referenced docs need some augmentation.

---

Internal previews

📄 File	🔗 Preview link
docs/core/diagnostics/distributed-tracing-builtin-activities.md	Built-in activities in .NET
docs/fundamentals/networking/telemetry/metrics.md	Networking metrics
docs/fundamentals/networking/telemetry/overview.md	Networking telemetry in .NET
docs/fundamentals/networking/telemetry/tracing.md	docs/fundamentals/networking/telemetry/tracing
docs/fundamentals/toc.yml	docs/fundamentals/toc

[samsp-msft]

Great content. Lets make the changes to the core telemetry example so you don't need to document how to modify it.

[antonfirsov]

@gewarren would you mind doing a language review on this? (Though I think it's mostly ok, so it's optional.)

[gewarren]

I'll wait to review the rest until you've run Acrolinx (see one of the comments I left).

[gewarren]

We've been trained not to use -ing words in headings and titles - see for example https://review.learn.microsoft.com/help/platform/metadata-required-articles?branch=main#title.

[gewarren]

Did you edit these files in VS Code? If so, it would be good to run Acrolinx on them to find a lot of the stuff that I would otherwise find. See https://review.learn.microsoft.com/en-us/help/platform/acrolinx-vscode-setup?branch=main#install-acrolinx-in-visual-studio-code.

[gewarren]

Suggested change

	In order to take advangage of the built-in metrics instrumentation, a .NET app needs to be configured to collect these metrics. This typically means transforming them for external storage and analysis, e.g., to monitoring systems.
	To take advantage of the built-in metrics instrumentation, a .NET app needs to be configured to collect these metrics. This typically means transforming them for external storage and analysis, for example, for monitoring systems.