Merge pull request #66102 from nikhita/add-optional-comment-tags

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

apiextensions: add optional comment tags

Adds `// +optional` comment tags to fields which are optional/omitempty for CRD types.

These tags are used for openapi generation:

0cf8f7e6ed/pkg/generators/openapi.go (L361-L362)

0cf8f7e6ed/pkg/generators/openapi.go (L81-L89)

**Release note**:

```release-note
NONE
```

api/openapi-spec/swagger.json

@@ -87333,6 +87333,9 @@
    },
    "io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.CustomResourceDefinition": {
     "description": "CustomResourceDefinition represents a resource that should be exposed on the API server.  Its name MUST be in the format \u003c.spec.name\u003e.\u003c.spec.group\u003e.",
+    "required": [
+     "spec"
+    ],
     "properties": {
      "apiVersion": {
       "description": "APIVersion defines the versioned schema of this representation of an object. Servers should convert recognized schemas to the latest internal value, and may reject unrecognized values. More info: https://git.k8s.io/community/contributors/devel/api-conventions.md#resources",