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
```