Add metrics configuration docs

[rosebyte]

Summary

Adds a concise Configure metrics with IConfiguration section to the metrics collection tutorial.

• Documents Generic Host configuration and explicit non-hosted DI registration.
• Covers metric scopes, listener-specific rules, Default, matching, and precedence.
• Adds a valid appsettings.json example.
• Clarifies that configuration filters instruments for IMetricsListener; it doesn't configure collection or export.
• Uses the merged implementation and MetricsConfigureOptionsTests from dotnet/runtime#90201 as the source of truth. No proposal APIs were copied from dotnet/runtime#85684.

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Internal previews

File	Preview link
docs/core/diagnostics/metrics-collection.md	Learn preview
docs/core/diagnostics/snippets/Metrics/appsettings.json	Learn preview

Build report

[Copilot]

Pull request overview

Adds documentation for configuring .NET metrics filters via IConfiguration in the metrics collection tutorial, including how hosted and non-hosted DI scenarios bind the Metrics configuration section and how rule scoping and precedence work.

Changes:

• Added a new “Configure metrics with IConfiguration” section to metrics-collection.md, including guidance on listener scoping, meter/instrument rules, and precedence.
• Added an appsettings.json snippet showing meter-level defaults with an instrument-level override.
• Updated the article ms.date.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
docs/core/diagnostics/metrics-collection.md	Adds the new configuration section, code sample, and rule explanation for metrics filtering via configuration.
docs/core/diagnostics/snippets/Metrics/appsettings.json	Adds a JSON configuration example referenced by the tutorial.

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