Automatic merge from submit-queue (batch tested with PRs 53743, 53564). 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>.

Polymorphic Scale Client

This PR introduces a polymorphic scale client based on discovery information that's able to scale scalable resources in arbitrary group-versions, as long as they present the scale subresource in their discovery information.

Currently, it supports `extensions/v1beta1.Scale` and `autoscaling/v1.Scale`, but supporting other versions of scale if/when we produce them should be fairly trivial.

It also updates the HPA to use this client, meaning the HPA will now work on any scalable resource, not just things in the `extensions/v1beta1` API group.

**Release note**:
```release-note
Introduces a polymorphic scale client, allowing HorizontalPodAutoscalers to properly function on scalable resources in any API group.
```

Unblocks #29698
Unblocks #38756
Unblocks #49504 
Fixes #38810