Support server-side apply

**What is the feature and why do you need it**:
Kubernetes [server-side apply](https://kubernetes.io/docs/reference/using-api/server-side-apply/) is meant to be the new standard of patching objects and managing fields. Today the Python client supports v18 API (v18.17.0a1), where server-side apply went [beta 2](https://kubernetes.io/blog/2020/04/01/kubernetes-1.18-feature-server-side-apply-beta-2/). We should explore what's missing to support the feature in this client.
- what API endpoints support SSA?
- what's the content-type to use SSA?
- how does client-go support SSA?

cc @fabianvf

Start with the linked Kubernetes server-side apply documentation, then review the Python client’s current support for Kubernetes v18 API and compare the relevant client-go support. Determine which API endpoints and content type are required; the work is done when the missing client support is identified and the implementation scope is clear.

Written by the indexing model from the issue text.