Add roles and test user guidance

[guardrex]

Fixes #31045

cc: @julioct ... My guesses on dealing with roles/role claims were good. The approach of NOT trying to fight the JSON serializer/deserializer to work with Claim arrays turns out to be the right way to go. Use of an anonymous type on the /roles endpoint side (backend server API) is fine, and using a custom RoleClaim type on the frontend is also good. These are the low-hanging-fruit happy paths 😄.

WRT other claim types, we're going to leave that to the devs to work out from this example. It's a straightforward update to this code to send all of the claims. The frontend code will take whatever is sent back and make user claims out of it. We might do more in this area down the road, but I need to get on with other work for now 🏃‍♂️😅. I'll take feedback from the community in the meantime.

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aspnetcore/blazor/security/webassembly/standalone-with-identity.md	Secure ASP.NET Core Blazor WebAssembly with ASP.NET Core Identity

[guardrex]

... and cc: @adrianjcalvert on this PR to see what's going in.

This will go live into the article by EOD. The sample app on the Blazor samples repo has already been updated ...

https://github.com/dotnet/blazor-samples/tree/main/8.0/BlazorWebAssemblyStandaloneWithIdentity

... BUT I forgot to update the README file. I'll do that in a few minutes. Done! 👍

... and also CC: to @famda-vestas on this.

... and @Ogglas.

I'm trying to notify everyone who asked.

[guardrex]

Ok ... cool ... glad to get this one in.

Thanks everyone! 🎉🍻

This will go ⚡ LIVE ⚡ in the article within a few hours.