Expose latest version via CLI, without updating

[lonix1]

I can use dotnet libman update to update all packages.

But who does that on a production system? It's important to 1) know what updates are available, 2) research the release notes, and then 3) update (and test).

So like other package managers, it would be nice to be able to simply list the latest versions; perhaps:

$ dotnet libman update --list