Add ASP.NET Core release notes for .NET 10 Preview 6

[Copilot]

This PR adds comprehensive ASP.NET Core release notes for .NET 10 Preview 6 based on the feature content provided in dotnet/AspNetCore.Docs#35602.

Changes Made

• Created /release-notes/10.0/preview/preview6/aspnetcore.md following the established format from previous preview releases
• Compiled and edited content from issue comments for clarity and simplicity
• Included all 10 major features for Preview 6:

Key Features Documented

1. Automatic eviction from memory pool - Memory pools now automatically release unused memory when applications are idle
2. Blazor WebAssembly preloading - New <LinkPreload /> component replaces link headers for better asset preloading
3. Blazor build producing javascript bundler friendly output - Support for webpack/rollup compatibility with WasmBundlerFriendlyBootConfig=true
4. Improved form validation for Blazor - Support for validating nested objects and collection items with [ValidatableType] attribute
5. NotFound works with streaming that has started - Enhanced error handling for streaming scenarios
6. Blazor diagnostics improvements - Top-level traces in Aspire dashboard and Application Insights
7. NavigationException switch behavior change - Updated default behavior and configuration switch naming
8. Add passkey support to ASP.NET Core Identity - WebAuthn and FIDO2 standards support for passwordless authentication
9. Minimal API Validation integration with IProblemDetailsService - Customizable error responses for validation
10. Unified validation APIs moved to extensions package - APIs moved to Microsoft.Extensions.Validation namespace

Content Structure

• Clear table of contents with anchor links
• Detailed feature descriptions with code examples
• "Why it matters" and "How to use" sections where applicable
• Community contributor acknowledgments
• Links to related documentation and breaking changes

The content follows the same markdown structure and writing style as existing preview release notes, ensuring consistency across the documentation.

Fixes #9964.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/dotnet/aspnetcore/pulls
  • Triggering command: curl -s REDACTED (http block)
• https://api.github.com/repos/dotnet/aspnetcore/search/issues
  • Triggering command: curl -s REDACTED (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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[danroth27]

Revise any statement that says circuit state persistence is automatic to clarify that only declared state is persisted. Avoid the use of "automatic" in this section.

[Copilot]

Revised the language to clarify that only declared state is persisted and removed all instances of "automatic" from the section. (5746985)

[danroth27]

Edit the content for clarity and simplicity.

[Copilot]

Edit the content for clarity and simplicity.

Edited the content throughout the document for clarity and simplicity. Simplified language, reduced verbosity, streamlined code examples, and made explanations more concise and user-friendly while maintaining accuracy. (b1b2f23)

[danroth27]

Add back the try/catch logic.

[Copilot]

Added back the try/catch logic to the memory pool code example. (5695157)