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lowercase node name in generated static pod name 

**What this PR does / why we need it**:
Cast appended node name to lowercase when generating static pod name on kubelet starting.

**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 #59801 

**Special notes for your reviewer**:
Not sure about how to deal with other illegal node names e.g. containing invalid no-alphabetic characters. Maybe just let it fail-hard is not a bad idea.
But considering that containing uppercase letter in the hostname is somehow a usual case even in the production environment of some companies, tolerating uppercase and cast it implicitly should be good.

**Release note**:

```release-note
force node name lowercase on static pod name generating
```