Merge pull request #54933 from php-coder/psp_introduce_new_api_group

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Introduce PodSecurityPolicy in the policy/v1beta1 API group

Types/constants are completely the same as in `extensions/v1beta1` except that they are located outside of the `extensions` API group.

**What this PR does / why we need it**:
This is the first step for migrating PSP-related stuff away of `extensions` group. See #43214 for more information.

Also it related to https://github.com/kubernetes/features/issues/5

**Example**:
```console
$ cat restricted2.yaml 
apiVersion: policy/v1beta1
kind: PodSecurityPolicy
metadata:
  name: restricted2
...
$ kubectl create -f restricted.yaml 
podsecuritypolicy "restricted2" created
$ kubectl get psp restricted2 -o yaml
apiVersion: extensions/v1beta1
kind: PodSecurityPolicy
...
```

**Release note**:
```release-note
The `PodSecurityPolicy` API has been moved to the `policy/v1beta1` API group. The `PodSecurityPolicy` API in the `extensions/v1beta1` API group is deprecated and will be removed in a future release.
```

examples/podsecuritypolicy/rbac/policies.yaml

@@ -1,4 +1,4 @@
-apiVersion: extensions/v1beta1
+apiVersion: policy/v1beta1
 kind: PodSecurityPolicy
 metadata:
   name: privileged
@@ -23,7 +23,7 @@ spec:
   - min: 1
     max: 65536
 ---
-apiVersion: extensions/v1beta1
+apiVersion: policy/v1beta1
 kind: PodSecurityPolicy
 metadata:
   name: restricted