Automatic merge from submit-queue

Let release_1_5 clientset include multiple versions of a group

Fix #35237 

This PR make versioned clientset to include multiple versions of a group. Currently only `batch` has `v1` and `v2alpha1`. The clientset interface now looks like:
```go
	BatchV2alpha1() v2alpha1batch.BatchV2alpha1Interface
	BatchV1() v1batch.BatchV1Interface
	// Deprecated: please explicitly pick a version if possible.
	Batch() v1batch.BatchV1Interface
```

Commit "update client-gen to say internalversion rather than unversioned" fixes https://github.com/kubernetes/kubernetes/issues/24481. 


cc @kubernetes/sig-api-machinery @soltysh @deads2k @nikhiljindal 



```release-note
release_1_5 clientset supports multiple versions of a group.
```