Merge pull request #62893 from hzxuzhonghu/mark-APIServiceSpec.CABundle-optional

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>.

mark APIServiceSpec.CABundle optional

xref: https://github.com/kubernetes/kubernetes/issues/60690#issuecomment-382842852
mark the caBundle field optional so openapi is accurate

**Release note**:

```release-note
NONE
```

api/openapi-spec/swagger.json

@@ -85393,7 +85393,6 @@
     "description": "APIServiceSpec contains information for locating and communicating with a server. Only https is supported, though you are able to disable certificate verification.",
     "required": [
      "service",
-     "caBundle",
      "groupPriorityMinimum",
      "versionPriority"
     ],
@@ -85539,7 +85538,6 @@
     "description": "APIServiceSpec contains information for locating and communicating with a server. Only https is supported, though you are able to disable certificate verification.",
     "required": [
      "service",
-     "caBundle",
      "groupPriorityMinimum",
      "versionPriority"
     ],