Automatic merge from submit-queue (batch tested with PRs 58444, 59283, 59437, 59325, 59449). 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>.

Update PriorityClassName API doc

**What this PR does / why we need it**: It updates the comment (and hence API doc) for PriorityClassName of PodSpec.

**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
NONE
```

/sig scheduling