Better selection mechanisms for packages during clone or at least get

[johnbelamaric]

Describe your problem

Say I want to kpt alpha rpkg clone. Right now, I need the PackageRevision name. This is painful, it requires me to run kpt alpha rpkg get, and find the right entry in the list. This is painful.

It would be nice to be able to use the package name and revision, and/or the latest-revision label. If I can't use those directly in clone, perhaps at least supporting them in rpkg get would help. That is, it would be nice to be able to use field selectors or to have a label on the PackageRevision with the package name and be able to use label selectors (but #3401). That would allow something like:

kpt alpha rpkg clone $(kubectl get packagerevision -l package-name=coredns-caching,package-revision=v4) -n default ...