add an option to list only packages with versions that cannot be determined

[ak1dd]

Description of the new feature / enhancement

When you run "winget update --all" and have packages with versions that cannot be determined you are recommended to "Use --include-unknown to see all results" IMO this is very vague and using --include-unknown simply seems to remove the recommendation message when you use it and further execution of "winget update --all" again shows the recommendation with no direction or explanation. It doesn't seem to "...see all results" in any way I understand.

Proposed technical implementation details

I have a lot of installed applications. I'd like to be able to do something like "winget list --unknown-only" and show just the packages with versions that cannot be determined and not have to sort through a huge list or parse it with something else. I could just pin them or find versions winget can determine. I'd like the recommendation to read something like "Use "winget list --unknown-only to see unknown results"