Relocate reference generation tooling from Kubernetes Incubator

[jimangel]

@mrbobbytables brought to my attention during the 1.14 cycle that the Kubernetes Incubator repo is sort of "pre-retirement."

Given that our reference-docs tooling lives there, we should consider moving it out to a SIG or Core repository described in the above link.

Also, since we rely heavily on those tools for the release process this might be a slightly larger undertaking to migrate. I don't see any need to make this an urgent priority, but wanted to open an issue for tracking.

TODO:

• PR fixes for: https://github.com/kubernetes/website/search?q=kubernetes-incubator%2Freference-docs&type=Code
• PR fixes for: https://github.com/kubernetes/community/tree/master/sig-docs#reference-docs
• We'll need to merge or hold: [WIP] Testing restyled kubectl ref docs kubernetes-sigs/reference-docs#82
• Update reg-gen codebase to reflect repo move. (https://github.com/kubernetes-sigs/reference-docs/search?q=kubernetes-incubator%2Freference-docs&unscoped_q=kubernetes-incubator%2Freference-docs)

/cc @tengqm @zacharysarah @makoscafee

[zacharysarah]

/cc @steveperry-53

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[mrbobbytables]

/remove-lifecycle rotten
ref: kubernetes/community#1922 (comment)