Expose metrics port for karmadactl installation

[whitewindmills]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:

Which issue(s) this PR fixes:
part of #5166

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

`karmadactl`: Expose the metrics port for PodMonitor.

[whitewindmills]

/cc @RainbowMango @chaosi-zju

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 69.56522% with 7 lines in your changes missing coverage. Please review.

Project coverage is 28.26%. Comparing base (7982275) to head (6158fd8).
Report is 2 commits behind head on master.

Files	Patch %	Lines
pkg/karmadactl/register/register.go	0.00%	7 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5169      +/-   ##
==========================================
+ Coverage   28.23%   28.26%   +0.02%     
==========================================
  Files         632      632              
  Lines       43566    43589      +23     
==========================================
+ Hits        12302    12321      +19     
- Misses      30366    30371       +5     
+ Partials      898      897       -1     

Flag	Coverage Δ
unittests	28.26% <69.56%> (+0.02%)	⬆️

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[liangyuanpeng]

suggest add a release-note for it,maybe:

karmadactl: exporting the metrics port for PodMonitor.

[RainbowMango]

Either have a release note or not, both OK to me.

[chaosi-zju]

/lgtm

[RainbowMango]

/approve
Thanks.

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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