Added missing metrics for .NET extensions.

[IEvangelist]

Summary

Added missing metrics for .NET extensions.

Contributes to #37411 and #37835

Tagging @iliar-turdushev and @davidfowl

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Internal previews

📄 File	🔗 Preview link
docs/core/diagnostics/built-in-metrics-aspnetcore.md	ASP.NET Core metrics
docs/core/diagnostics/built-in-metrics-diagnostics.md	.NET extensions metrics
docs/core/diagnostics/built-in-metrics-system-net.md	System.Net metrics
docs/core/diagnostics/built-in-metrics.md	Built-in metrics in .NET
docs/core/diagnostics/diagnostic-health-checks.md	docs/core/diagnostics/diagnostic-health-checks
docs/core/diagnostics/diagnostic-resource-monitoring.md	Resource monitoring

[tdykstra]

LGTM aside from the typo noted.

[iliar-turdushev]

Since Microsoft.AspNetCore.HeaderParsing is a part of dotnet/extensions, shouldn't we move description of this meter and its metrics to ".NET extensions metrics" article? @IEvangelist

[IEvangelist]

That's a fair question, but I'd argue "no". This package, while it ships out of dotnet/extensions is specific to ASP.NET Core and isn't workload agnostic, therefore it belongs with the other ASP.NET Core specific metrics (otherwise we're shipping our org chart so to speak). I suppose we should defer to @davidfowl and @joperezr, but I feel very strongly about this.