add new command label

[zhzhuang-zju]

What type of PR is this?
/kind feature

What this PR does / why we need it:
add new command label

Which issue(s) this PR fixes:
Parts of #5249

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

`karmadactl`: add a new command `label` to update the labels on a resource

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 31.16%. Comparing base (c9e0ad7) to head (8b21a65).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/karmadactl/karmadactl.go	0.00%	5 Missing ⚠️
pkg/karmadactl/label/label.go	0.00%	4 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5453      +/-   ##
==========================================
+ Coverage   31.15%   31.16%   +0.01%     
==========================================
  Files         640      641       +1     
  Lines       44417    44426       +9     
==========================================
+ Hits        13837    13845       +8     
+ Misses      29580    29577       -3     
- Partials     1000     1004       +4     

Flag	Coverage Δ
unittests	31.16% <0.00%> (+0.01%)	⬆️

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[zhzhuang-zju]

assign @RainbowMango

[zhzhuang-zju]

/retest

[RainbowMango]

/lgtm
/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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• OWNERS [RainbowMango]

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