Automatic merge from submit-queue (batch tested with PRs 53575, 53794). 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>.
Add e2e test case for downward API exposing pod UID
**What this PR does / why we need it**:
Pod UID is added to downward API env var in #48125 for 1.8. This PR adds a e2e test case for it.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
ref: #48125
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```
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