Automatic merge from submit-queue
add --as-group option to cli
The usecase of this change:
When a super user grant some RBAC permissions to a group, he can use
--as--group to test whether the group get the permissions.
Note that now we support as-groups, as-user-extra in kubeconfig file after this change.
**Release note**:
```NONE
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@liggitt
294c6362bd