Remove Auth validation when Form File upload

[brunolins16]

Today, a Minimal endpoint does not allow a Form File(s) upload when any kind of authentication is detected, and a request will fail for all the following scenarios:

• A client certificate is present, or
• A Authorization header is set, or
• Has cookies

This behavior was initially decided since we do not have any kind of in-box antiforgery mechanism for Minimal APIs.

This PR is related to our decision the change it and remove all these validations (same behavior existing in API Controllers) and allow all Form File(s) requests as default.

In addition, the documentation will be improved to show how to manually add support for antiforgery scenarios using IAntiforgery services.

Closes #38630

[blowdart]

Please link to docs PR :)

[davidfowl]

LGTM, what @blowdart said 😄

[brunolins16]

Merging this PR and I have dotnet/AspNetCore.Docs#26386 in review for documentation changes.

[ghost]

@brunolins16, this change will be considered for inclusion in the blog post for the release it'll ship in. Nice work!

Please ensure that the original comment in this thread contains a clear explanation of what the change does, why it's important (what problem does it solve?), and, if relevant, include things like code samples and/or performance numbers.

This content may not be exactly what goes into the blog post, but it will help the team putting together the announcement.

Thanks!