Automatic merge from submit-queue (batch tested with PRs 61963, 64279, 64130, 64125, 64049). 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>.

Make serverAddressByClientCIDRs in discovery API optional

**What this PR does / why we need it**:
See https://github.com/kubernetes/kubernetes/issues/61868

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #61868

**Special notes for your reviewer**:
WIP: I'm having trouble updating swagger-spec using our update scripts. Thinking about removing swagger-spec from our code base as it has long passed deprecation. Sending this PR now to see the test results. 

**Release note**:

```release-note
Property `serverAddressByClientCIDRs` in `metav1.APIGroup` (discovery API) now become optional instead of required
```

/sig api-machinery