Guidance and migration for Duende IdS

[guardrex]

Fixes #22355
Addresses dotnet/aspnetcore#32881
Addresses #22045

This at least gets the ball rolling ... but there are potentially a few little devils 😈 in the details ...

• Not sure on the presence and phrasing of public DbSet<Key> Keys { get; set; } in the migration topic.
• I added Duende to the ToC with a cross-link to their docs. This PR keeps the existing ToC cross-link to IdentityServer4 docs. Do u want to keep that cross-link in the ToC?
• Hao, your PU PR didn't include the license text AFAICT ... it might have been a different project template PR tho. I took a shot at wording lingo here for docs.
• I can't quite test all of the Blazor guidance YET. I do plan to do so tho ... either in the RC period or after GA (possibly as late as January) as part of either testing for 6.0 GA with test apps or for my UE passes when I get back to them early next year. Until then tho, I recommend that we merely take reader feedback on the Blazor IdS topic and see if we get reports of 😈 cropping up.

@Rick-Anderson ... There's one topic (the last one for these updates AFAICT) that I didn't address here ...

Introduction to Identity on ASP.NET Core
https://docs.microsoft.com/en-us/aspnet/core/security/authentication/identity?view=aspnetcore-5.0&tabs=visual-studio

It uses the prior versioning approach to Whole-topic Versioning ... call it ... er ... Flip-mode Versioning™ 😄. Therefore, I'll probably/possibly butcher how you would want to handle the update. It's a simple update tho for the one IdS line after the versioning is refactored. It just needs ...

[!INCLUDE[](~/includes/IdentityServer4.md)]

... changed to ...

[!INCLUDE[](~/includes/DuendeIdentityServer.md)]

... for >=6.0 coverage. That INCLUDE file is on this PR, so a followup PR will have access to it. If you'd like me to try and fix the versioning by refactoring it on this PR, ok ... I'll give it a shot. 👂

[HaoK]

Hao, your PU PR didn't include the license text AFAICT ... it might have been a different project template PR tho. I took a shot at wording lingo here for docs.

@blowdart do we need to still include license text anywhere? I don't think I updated any new license text, I did add a new readme that gets created on project creation in the template: see https://github.com/dotnet/aspnetcore/blob/main/src/ProjectTemplates/Web.ProjectTemplates/content/ComponentsWebAssembly-CSharp/Server/Readme.txt

[blowdart]

No, but example the popup text to say Duende IdentityServer everywhere (line 2) and expand AAD to say Azure ActiveDirectory.

Also, that aka.ms link should be for IS, not AAD, and it's on the AAD line which is weird.

[guardrex]

Holding for @Rick-Anderson to advise on Introduction to Identity on ASP.NET Core ... either to take care of it separately after this PR is merged, or I'll take a 🔪 stab at it here.

[HaoK]

https://aka.ms/aspnetidentityserver goes to our identity readme (AAD line)
https://aka.ms/identityserverlicense goes to the IS docs (last line)

[Rick-Anderson]

Holding for @Rick-Anderson to advise on Introduction to Identity on ASP.NET Core ... either to take care of it separately after this PR is merged, or I'll take a 🔪 stab at it here.

Either way is fine.

[guardrex]

@Rick-Anderson ... Ok, I'll let you handle that one. I opened #23048 to cover it.

I'll sleep on this one 🛌💤, make final touches, and merge in the morning (8/18).