Automatic merge from submit-queue (batch tested with PRs 43505, 45168, 46439, 46677, 46623)

Add TPR to CRD migration helper.

This is a helper for migrating TPR data to CustomResource. It's rather hacky because it requires crossing apiserver boundaries, but doing it this way keeps the mess contained to the TPR code, which is scheduled for deletion anyway.

It's also not completely hands-free because making it resilient enough to be completely automated is too involved to be worth it for an alpha-to-beta migration, and would require investing significant effort to fix up soon-to-be-deleted TPR code. Instead, this feature will be documented as a best-effort helper whose results should be verified by hand.

The intended benefit of this over a totally manual process is that it should be possible to copy TPR data into a CRD without having to tear everything down in the middle. The process would look like this:

1. Upgrade to k8s 1.7. Nothing happens to your TPRs.
1. Create CRD with group/version and resource names that match the TPR. Still nothing happens to your TPRs, as the CRD is hidden by the overlapping TPR.
1. Delete the TPR. The TPR data is converted to CustomResource data, and the CRD begins serving at the same REST path.

Note that the old TPR data is left behind by this process, so watchers should not receive DELETE events. This also means the user can revert to the pre-migration state by recreating the TPR definition.

Ref. https://github.com/kubernetes/kubernetes/issues/45728