WsFederation Wtrealm is required but it is a nullable string on WsFederationOptions

[eerhardt]

          @halter73 @Tratcher - any thoughts here? Why is `Options.Wtrealm` annotated as `string?` when `WsFederationMessage.Wtrealm` is a non-nullable `string`? Do we have our nullable annotations incorrect in ASP.NET?

Originally posted by @eerhardt in #50218 (comment)

[halter73]

Should we close this now that AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet#2240 has been opened?

[eerhardt]

I think we can use this to track removing the !s added in #50218. All three of them should be able to be removed once we get a build with AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet#2241 in it.

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.