Restarting sidecar containers during Pod termination

<!-- 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 --> Sidecar containers should be restarted if they exit prematurely when a Pod is terminated to ensure that they are running while the containers that should terminate prior to its termination are still running. This feature was originally planned for beta release in the initial KEP, but after further analysis, we decided to postpone and introduce a separate feature gate for it.