StatefulSet Slice

<!-- This section is incredibly important for producing high-quality, user-focused documentation such as release notes or a development roadmap. It should be possible to collect this information before implementation begins, in order to avoid requiring implementors to split their attention between writing release notes and implementing the feature itself. KEP editors and SIG Docs should help to ensure that the tone and content of the Summary section is useful for a wide audience. A good summary is probably at least a paragraph in length. Both in this section and below, follow the guidelines of the [documentation style guide]. In particular, wrap lines to a reasonable length, to make it easier for reviewers to cite specific portions, and to minimize diff churn on updates. [documentation style guide]: https://github.com/kubernetes/community/blob/master/contributors/guide/style-guide.md --> The goal of this feature is to allow a StatefulSet to be migrated (cross namespace, cross cluster, split into segments) without disrupting the underlying application. A StatefulSet of N replicas implicitly numbers pods from ordinal 0 to N-1. The end ordinal (N-1) can be controlled with the replicas field. The goal of this feature is to allow a StatefulSet’s first ordinal to start from any natural number k. This enables StatefulSet ordinals from k to N+k-1