Support updating workloadVersion

[jjonescz]

dotnetup install preview --update-global-json updated my sdk.version but not sdk.workloadVersion, now I have to update that manually.
FWIW, I don't need it to run dotnet workload restore or anything, I just want it to find the version number and put it to my global.json.

[nagilson]

Migrating to an issue, thanks for reporting this. Good idea. #54691

[marcpopMSFT]

Hmm, the challenge here is that this works well for stable versions but for the previews, the workload version and the SDK version are not really connected (other than both being the same preview). To make that work here, we'd have to install the sdk first, then get the workload set from the dotnet workload search version output, and then update.