Add Microsoft.Identity.Web migration guide to 3.1->5.0 documentation

[JunTaoLuo]

Issue description

In addition to updating existing docs for AAD in https://github.com/dotnet/AspNetCore.Docs/issues/19809, we also need to include a migration guide for users going from 3.1 to 5.0. The following information would be helpful in constructing the migration doc:

• https://github.com/AzureAD/microsoft-identity-web/wiki/Web-Apps#with-azure-ad
• https://github.com/AzureAD/microsoft-identity-web/wiki/Web-APIs#why-to-use-microsoftidentityweb-in-web-apis

Looking at our docs at https://docs.microsoft.com/en-us/aspnet/core/migration/31-to-50?view=aspnetcore-3.1&tabs=visual-studio, it seems like the AAD migration doc belongs in the list of breaking changes.

Software versions

Check the .NET target framework(s) being used, and include the version number(s).

• [x] .NET Core (.NET 5 replaces both)
• [x] .NET Framework (.NET 5 replaces both)
• [ ] .NET Standard

If using the .NET Core SDK, include dotnet --info output. If using .NET Framework without the .NET Core SDK, include info from Visual Studio's Help > About Microsoft Visual Studio dialog.

dotnet --info output or About VS info

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[JunTaoLuo]

cc @Tratcher @jmprieur

[mkArtakMSFT]

@JunTaoLuo assigning to you to handle as necessary.

[JunTaoLuo]

I think @jmprieur would be the best to provide these docs. I think most of the information is already available at https://github.com/AzureAD/microsoft-identity-web/wiki and https://developer.microsoft.com/en-us/microsoft-365/blogs/microsoft-identity-web-is-now-generally-available/#:~:text=We're%20excited%20to%20announce,Web%20is%20now%20generally%20available.&text=Web%20brings%20a%20renewed%2C%20simplified,Graph%20or%20other%20web%20APIs. There's potentially work in synthesizing this information into aspnetcore relevant docs.

[jmprieur]

Yes: the following wiki pages explain how to migrate:

• https://github.com/AzureAD/microsoft-identity-web/wiki/web-apps (for web apps)
• https://github.com/AzureAD/microsoft-identity-web/wiki/web-apis for web apis

We also have the ASP.NET Core web app and web API tutorials which explain the migration:

• https://github.com/Azure-Samples/active-directory-aspnetcore-webapp-openidconnect-v2/tree/master/1-WebApp-OIDC/1-1-MyOrg#option-2-create-the-sample-from-the-command-line
• https://github.com/Azure-Samples/active-directory-dotnet-native-aspnetcore-v2/tree/master/1.%20Desktop%20app%20calls%20Web%20API#how-was-the-code-created