Script to remove old .NET SDK Installs

[patrick-king]

It would be nice to have a script that could look at a list of valid .NET SDK versions, and remove all other versions on the local machine.

[patrick-king]

This could be a powershell script that calls for a list of supported versions stored in Azure Storage with public access. Or it could just scrape the GitHub page of .NET SDK's to get the supported versions.
V1 will leverage a hard-coded array of supported versions. Then we can expand if time permits.