Automatic merge from submit-queue
move api.ObjectReference.ObjectKind to pkg/api/ref.go
This is needed to convert k8s components to use versioned clientset.
To let components use versioned client, we need to convert `pkg/client/record` to v1, which depends on `pkg/api/ref.go`, so we need to make a `pkg/api/v1/ref.go`. And this [line](https://github.com/kubernetes/kubernetes/blob/master/pkg/api/ref.go#L44) requires v1.ObjectReference to be a runtime.Object. Moving `api.ObjectReference.ObjectKind` to `pkg/api/ref.go` will make the writing a conversion script easier because all the necessary changes will be restricted in `ref.go`.
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