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>.
adds generic scaler to kubectl
**What this PR does / why we need it**:
this PR adds generic scaler to kubectl. The implementation uses a polymorphic scale client capable of operating against scale subresources which can be found here https://github.com/kubernetes/client-go/tree/master/scale
**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 #
**Release note**:
```release-note
NONE
```
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