Switch openapi-gen from k8s.io/code-generator to k8s.io/kube-openapi

[RainbowMango]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

The openapi-gen has been removed from k8s.io/code-generator by kubernetes/kubernetes#123529 because it is redundant with the one in k8s.io/kube-openapi.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
We are going to bump Kubernetes dependencies to v1.30, this PR solves one of the blockers.

Does this PR introduce a user-facing change?:

NONE

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.21%. Comparing base (c0c5569) to head (7eba226).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5111      +/-   ##
==========================================
- Coverage   28.22%   28.21%   -0.01%     
==========================================
  Files         632      632              
  Lines       43556    43556              
==========================================
- Hits        12293    12290       -3     
- Misses      30367    30369       +2     
- Partials      896      897       +1     

Flag	Coverage Δ
unittests	28.21% <ø> (-0.01%)	⬇️

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[RainbowMango]

/assign @chaunceyjiang

[RainbowMango]

ping @chaunceyjiang

[chaunceyjiang]

/assign

[chaunceyjiang]

Successfully tested on Mac M1.

/lgtm

[karmada-bot]

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