FEATURE REQUEST: Create a new version in the apps group for the core workloads API.
When we advance the core workloads API (DaemonSet, Deployment, ReplicaSet, and StatefulSet) to v1, we want them to advance as a group and be (where possible) consistent. Prior to doing so, we would like to make any API incompatible changes. In particular we will

• bump Deployment and StatefulSet to apps/v1beta2 (Add a new API version apps/v1beta2 #48746) @janetkuo
• bump ReplicaSet to apps/v1beta2 (Add apps/v1beta2.ReplicaSet #49238) @janetkuo
• bump DaemonSet to apps/v1beta2 (Add v1beta2.DaemonSet #49071) @foxish
• deprecate .spec.rollbackTo, and remove the /rollback subresource of apps/v1beta2 deployment or modify it such that the controller is not required to modify its own spec. (Deprecate Deployment .spec.rollbackTo field  #49340) @janetkuo
• add a /scale subresource for StatefulSet (StatefulSet scale subresource #49168) @crimsonfaith91
• remove the templateGeneration feild of DaemonSet (Cleanup DaemonSet templateGeneration #49454) @dixudx
• change the StatefulSet observedGeneration from a pointer to an int for consistency. (change apps/v1beta2 StatefulSet observedGeneration from a pointer to an int for consistency #49607) @dixudx
• review the API objects for consistency, and (where appropriate) make changes to bring them into alignment (modifying field names a necessary).
• ensure that the defaults and validation are consistent and appropriate across all controllers.
• deprecate core workloads API versions under /extensions
• enable apps/v1beta2 by default and remove WIP marks after API changes is done

We may find other incompatible changes that are required prior to promotion, and we would like to make them in this version, prior to releasing it. When the community is satisfied with the API surface, as contained in this version, and it is stable, we would like to promote all of the core workloads API to GA by moving the contained API to v1.

kubernetes/enhancements#353
/kind feature