Automatic merge from submit-queue. 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>.
Introduce new `VolumeAttachment` API Object
**What this PR does / why we need it**:
Introduce a new `VolumeAttachment` API Object. This object will be used by the CSI volume plugin to enable external attachers (see design [here](https://github.com/kubernetes/community/pull/1258). In the future, existing volume plugins can be refactored to use this object as well.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: Part of issue https://github.com/kubernetes/features/issues/178
**Special notes for your reviewer**:
None
**Release note**:
```release-note
NONE
```
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 #49504Fixes#38810
This introduces a polymorphic scale client capable of operating against
scale subresources which return different group-versions of Scale. The
scale subresources may be in group-versions different than the scale
itself, so that we no longer need a copy of every scalable resource in
the extensions API group.
To discovery which Scale group-versions go to which subresources,
discovery is used.
The scale client maintains its own internal versions and conversions to
several external versions, with a "hub" version that's a copy of the
autoscaling internal version.
It currently supports the following group-versions for Scale subresources:
- extensions/v1beta1.Scale
- autoscaling/v1.Scale
Automatic merge from submit-queue (batch tested with PRs 51956, 50708)
Move autoscaling/v2 from alpha1 to beta1
This graduates autoscaling/v2alpha1 to autoscaling/v2beta1. The move is more-or-less just a straightforward rename.
Part of kubernetes/features#117
```release-note
v2 of the autoscaling API group, including improvements to the HorizontalPodAutoscaler, has moved from alpha1 to beta1.
```
Automatic merge from submit-queue (batch tested with PRs 49488, 50407, 46105, 50456, 50258)
Enable caching successful token authentication
Resolves#50472
To support revocation of service account tokens, an etcd lookup of the token and service account is done by the token authenticator. Controllers that make dozens or hundreds of API calls per second (like the endpoints controller) cause this lookup to be done very frequently on the same objects.
This PR:
* Implements a cached token authenticator that conforms to the authenticator.Token interface
* Implements a union token authenticator (same approach as the union request authenticator, conforming to the authenticator.Token interface)
* Cleans up the auth chain construction to group all token authenticators (means we only do bearer and websocket header parsing once)
* Adds a 10-second TTL cache to successful token authentication
```release-note
API server authentication now caches successful bearer token authentication results for a few seconds.
```
