Automatic merge from submit-queue
Move StorageClass to a storage group
We discussed the pros and cons in sig-api-machinery yesterday. Choosing a particular group name means that clients (including our internal code) require less work and re-swizzling to handle promotions between versions. Even if you choose a group you end up not liking, the amount of work remains the same as the incubator work case: you move the affected kind, resource, and storage.
This moves the `StorageClass` type to the `storage.k8s.io` group (named for consistency with authentication, authorization, rbac, and imagepolicy). There are two commits, one for manaul changes and one for generated code.