[codegen] Operator/Watcher codegen for non-owned resources

[IfSentient]

The CLI should have a way to import non-owned resources (say, with definitions in another repository) and build watchers and an operator using them the same way it currently works for grafana-app-sdk project component add operator with kinds defined in-repo.

This should either support pointing at the kind definition in a remote location, and/or pointing at go definitions.