Add missing supports for kubernetes client stable and gold

according to new [kubernetes client guidelines](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/csi-new-client-library-procedure.md#client-capabilities) python client is beta support and has silver capabilities. We are almost there to have gold capabilities and stable support. missing parts are:

Gold:
- [ ] Support attach, port-forward calls
- [ ] Proto encoding
- [ ] Generated examples #252 #219

Stable:
- [ ] N documented users of the library
- [ ] Support level documented per-platform
- [ ] Deprecation policy (backwards compatibility guarantees documented)
- [ ] Release process well documented

未提及任何儲存庫檔案或測試。先從連結的 Kubernetes 用戶端指南以及參照的 issue #252 和 #219 開始，接著判定每項未勾選的 Gold 和 Stable 要求如何對應至用戶端；完成表示列出的每項功能和文件需求都已完成。

由索引模型根據 Issue 內容生成。