Minimal API validation integration with `IProblemDetailsService` -Docs

[tdykstra]

See ttps://github.com//issues/35602#issuecomment-3053683158

[Additional info from WadePickett below]

Looking over this quickly, some candidates to consider for adding the new info about Minimal API Validation integration with IProblemDetailsService:

aspnetcore/fundamentals/minimal-apis.md

This is the main quick reference for Minimal APIs, and it has a section on "Validation support in Minimal APIs" that currently describes validation attributes, enabling validation, and error responses. This section should be updated to mention that error responses can now be customized using an IProblemDetailsService implementation.

aspnetcore/fundamentals/minimal-apis/responses.md

This file covers how to create and customize responses in Minimal API apps. It would be appropriate to add a subsection or note explaining that validation error responses can now be customized via IProblemDetailsService.

---

Associated WorkItem - 473958

[wadepickett]

@tdykstra, just a heads up, I'll take this one.