add example to modify headers in Minimal APIs

[timdeschryver]

Fixes #34471

• Adds an example on how to modify headers to quick reference and create response pages
• Adds example on Problem details in the create response page, which was added in v9 https://learn.microsoft.com/en-us/aspnet/core/release-notes/aspnetcore-9.0?view=aspnetcore-9.0#problem-and-validationproblem-result-types-support-construction-with-ienumerablekeyvaluepairstring-object-values

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Internal previews

📄 File	🔗 Preview link
aspnetcore/fundamentals/minimal-apis.md	aspnetcore/fundamentals/minimal-apis
aspnetcore/fundamentals/minimal-apis/responses.md	aspnetcore/fundamentals/minimal-apis/responses

[wadepickett]

Great! Well done. All I added was an update to the ms.date doc meta data so folks could see the topic has been updated. Thanks @timdeschryver!

[wadepickett]

Perfect!

[wadepickett]

Just realized I put 2024 in the date rather than 2025 out of habit. Fixed with #34671