Some `kwctl` subcommands need `registry://` while others don't

[viccuad]

Installing policies from artifacthub.io I realized the following:

$ kwctl pull ghcr.io/kubewarden/policies/safe-labels:v0.1.13 # as printed in artifacthub's install button, note no registry://
$ $ kwctl scaffold manifest -t ClusterAdmissionPolicy ghcr.io/kubewarden/policies/safe-labels:v0.1.13
Error: relative URL without a base

This is true for other subcommands too:

$ kwctl rm ghcr.io/kubewarden/policies/safe-labels:v0.1.13
Error: relative URL without a base
$ kwctl rm registry://ghcr.io/kubewarden/policies/safe-labels:v0.1.13