Just do all doc generation in the hack::util::gen-docs instead of spread
around. We also only track the generated docs in a single file for the
whole tree.
Right now, our doc generation scripts notice if you make changes and
don't regen docs, don't include new docs, etc. But they miss it if your
changes should have REMOVED a doc. Both kubectl-apiversion and
kubectl-clusterinfo should have been removed, but weren't.
This patch starts tracking all generated doc files and will cause
problems if files should be removed and aren't.
