SDKAnalysisLevel should call out the fact that it ages out

### Describe the issue or suggestion

https://learn.microsoft.com/en-us/dotnet/core/project-sdk/msbuild-props#sdkanalysislevel. 

During the design of the SDKAnalysisLevel feature we said it'll age out in 3 releases, namely 11.0.100 only has to respect up to 8.0.100 the most. 
12.0.100, features that could be disabled by 8.0.100 will no longer be disabled. 

cc @baronfel 