Automatic merge from submit-queue (batch tested with PRs 54875, 54813, 54595, 54947, 54766). 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>.

extra_sans option added to load balancer

Also cleaned up kubernetes-master charm to use the new method of determining a certificate has changed.


**What this PR does / why we need it**:
Adds an option for the load balancer charm to add extra SAN entries to the generated certificate used by nginx.
**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 #

**Special notes for your reviewer**:

**Release note**:

```release-note
Added extra_sans config option to kubeapi-load-balancer charm. This allows the user to specify extra SAN entries on the certificate generated for the load balancer.
```