Blazor security BWA with Identity components 8.0

[guardrex]

Fixes #30976
Addresses #28161

We can add more 🍖 if you wish (e.g., is there additional configuration to call out?), but the most important changes look merely to be ...

• Update the Authentication Types to just None and Individual Accounts.
• Version out the scaffolding guidance and remarks on Identity components and SignInManager/UserManager in the Blazor security overview article.
• Version out the scaffolding guidance in the Blazor server security doc.
• Version out the scaffolding guidance in the main doc set's Scaffolding article. NOTE: The article uses Whole-topic Versioning, so it's versioned out by making a copy of the entire 6.0 content block and deleting the bits to drop for >=8.0. They have a new INCLUDE file add-on process, but I'm not familiar with that approach and don't have time to learn and implement it because I'm up against the hard deadline for release with a lot of work to do yet 🏃‍♂️.
• Includes several of Jeremy's blog post comments.

NOTES:

• Updates to What's New guidance will be made on a separate PR later.
• I've opened an issue at Blazor BWA external/social login guidance 8.0 #30994 to create a new section for external/social identity providers. I'll get to that as soon as I can, but I think it will be after release.
• Dan ... For the Migration article, I assume that we're not going to provide a step-by-step conversion from scaffolded Razor Pages auth pages to Identity components along with all of the changes that are being introduced for BWA Individual account security. Is this a case where we'll 🏈 punt to the 🦖 GooberRex Migration Approach™ 🙈😆? ... Create a new BWA with Individual Accounts and copy your bits over to it. Even if you want full step-by-step guidance, I'll need to open an issue and address it later. There's no way it can be written between now and release.

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Internal previews

📄 File	🔗 Preview link
aspnetcore/blazor/security/index.md	ASP.NET Core Blazor authentication and authorization
aspnetcore/blazor/security/server/index.md	[Visual Studio](https://review.learn.microsoft.com/en-us/aspnet/core/blazor/security/server/index?branch=pr-en-us-30977)
aspnetcore/security/authentication/scaffold-identity.md	Scaffold Identity in ASP.NET Core projects