Automatic merge from submit-queue (batch tested with PRs 52477, 52790, 52798). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>..

conversion-gen: make staging dirs independent of living in vendor/

The `+k8s:conversion-gen` tags included the package directory inside of kube's vendor dir. This
makes them invalid when we publish staging repos.

Without this PR our sample-apiserver example code-generation is broken once published.