[.NET 10] Emphasize scope of `AddValidation()` on built-in validation support for minimal APIs

### Is there an existing issue for this?

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### Is your feature request related to a problem? Please describe the problem.

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### Describe the solution you'd like

It might be useful to emphasize at https://learn.microsoft.com/en-us/aspnet/core/release-notes/aspnetcore-10.0?view=aspnetcore-9.0#enable-built-in-validation-support-for-minimal-apis that `UnmappedMemberHandling` by default is set to `Skip`, even when adding `builder.Services.AddValidation();`. This might seem strange when you assume that adding the validation service will just validate the whole incoming JSON with the object type.

To take things further, it might even make more sense to call it `AddAnnotationValidation` instead of `AddValidation` because it's really scoped to a small part, and it isn't responsible for all the validation, like unmatched (query) parameters, or enums.

### Additional context

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