Automatic merge from submit-queue (batch tested with PRs 66780, 67330). 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>.
Changed admission controller to allow volume expansion for all volume plugins
**What this PR does / why we need it**:
There are two motivations for this change:
1. CSI plugins are soon going to support volume expansion. For such plugins, admission controller doesn't know whether the plugins are capabale of supporting volume expansion or not.
2. Currently, admission controller rejects PVC updates for in-tree plugins that don't support volume expansion (e.g., NFS, iSCSI). This change allows external controllers to expand volumes similar to how external provisioners are accommodated.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
This PR mimics the behavior of the PV controller when PVs are provisioned externally by logging and setting a new event for PVs that are being expanded externally. As SIG Storage is planning new types of operations on PVs, it may make more sense to a have a single event for all actions taken by external controllers.
**Release note**:
```release-note
The check for unsupported plugins during volume resize has been moved from the admission controller to the two controllers that handle volume resize.
```
/sig storage
/assign @gnufied @jsafrane @wongma7
There are two motivations for this change:
(1) CSI plugins are soon going to support volume expansion. For such
plugins, admission controller doesn't know whether the plugins are
capabale of supporting volume expansion or not.
(2) Currently, admission controller rejects PVC updates for in-tree plugins
that don't support volume expansion (e.g., NFS, iSCSI). This change allows
external controllers to expand volumes similar to how external provisioners
operate.
