Umbrella-Issue: kubeflow/manifests#1769

PodDefaults Webhook

Current manifests structure

.
├── bootstrap
│   ├── base
│   └── overlays
│       └── application
└── webhook
    ├── base
    ├── overlays
    │   ├── application
    │   └── cert-manager
    └── v3

Explanation

• bootstrap is a custom solution for creating a cert for the poddefaults webhook. I can't find the code for that solution in this repo. Instead of maintaining such code, we should rely on cert-manager.
• webhook/v3: Combines application and cert-manager overlays. Since we now rely on plain kustomize, let's remove v3 and use the standard base and overlays structure of kustomize.
• webhook/overlays/application: Adds an Application CR resource for the poddefaults webhook. We want to remove Application CRs, so this is a good opportunity to do so.
• webhook/overlays/cert-manager: Add a cert-manager certificate for the poddefault webhook. This is the only useful overlay and the one that should remain.

Recommended end state

    ├── base
    ├── overlays
        └── cert-manager