Automatic merge from submit-queue. 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>.
fed: Move cluster generator & constants from kubectl to kubefed pkg
This will ensure the history of the federation-only files can be cheaply retained during the branch filtering that will occur for #52992.
cc: @kubernetes/sig-multicluster-pr-reviews
/sig multicluster
/area federation
/assign irfanurrehman shashidharatd
/release-note-none