Dotnet-counters docs updates w.r.t UI and list of counters

[rcj1]

Summary

• Updated the UI in the dotnet-counters docs to reflect the more modern UI.
• Removed dotnet-counters list and instead directed users to the appropriate Learn page.
• Opened a PR in dotnet/diagnostics to indent tag sets such as those under gc.heap.generation data by an additional tab; this change is also reflected here in the docs.
  See dotnet-counters gc.heap.generation output diagnostics#4935

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Internal previews

📄 File	🔗 Preview link
docs/core/diagnostics/debug-highcpu.md	Debug high CPU usage in .NET Core
docs/core/diagnostics/debug-memory-leak.md	Debug a memory leak tutorial
docs/core/diagnostics/debug-threadpool-starvation.md	Debug ThreadPool starvation
docs/core/diagnostics/dotnet-counters.md	Investigate performance counters (dotnet-counters)
docs/core/diagnostics/metrics-collection.md	docs/core/diagnostics/metrics-collection
docs/core/diagnostics/metrics-instrumentation.md	Creating metrics

[noahfalk]

Above the pre-reqs said .NET SDK 6.0. We should change that to 9.0 to match what is shown.

[noahfalk]

Above the pre-reqs say SDK 3.1. We should change that to SDK 9.0 since we are showing newer behavior.

[rcj1]

If people use an older version it will still work with a different UI, correct? Then perhaps we should just leave it so as not to discourage people from trying just because they have an older SDK. We could add a note either here or up higher saying that with older SDKs your UI may look different, in fact we already will with my change.

[noahfalk]

If people use an older version it will still work with a different UI, correct?

Yep.

We could add a note either here or up higher saying that with older SDKs your UI may look different, in fact we already will with my change.

I'm good as long as somewhere we make it clear for the readers how to reproduce what the tutorial is showing. That sounds fine to me.