KEP-4951: Configurable tolerance for HPA

[jm-franc]

Add KEP-4951: Configurable tolerance for HPA

Issue link: https://github.com/kubernetes/enhancements/issues/4951

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[jm-franc]

Excellent work @jm-franc, thank you!

I left some suggestions in the comments, feel free to use them or tweak them further. I skipped the sections that are needed for Beta, since we're still a ways off (even the Alpha ones may be premature).

I think we can merge the end result as-is, and then work with the sig to get it to the implementable state.

Thank you for all those suggestions Patryk, I've merged all of them. I'm now sending this KEP for review.

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This pull-request has been approved by: jm-franc Once this PR has been reviewed and has the lgtm label, please assign gjtempleton for approval. For more information see the Kubernetes Code Review Process.

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[jm-franc]

/assign @gjtempleton

Assigning to Guy for review/approval.