Upload code coverage to Codecov

[RainbowMango]

What type of PR is this? /kind cleanup

What this PR does / why we need it: This PR enables code coverage and upload to Codecov.

Which issue(s) this PR fixes: Fixes #

Special notes for your reviewer: Refer:

• https://github.com/codecov/codecov-action
• Coverage Report: https://app.codecov.io/gh/karmada-io/karmada/tree/pr_upload_coverage/pkg

Does this PR introduce a user-facing change?:

NONE

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@ed13e66). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2575   +/-   ##
=========================================
  Coverage          ?   21.83%           
=========================================
  Files             ?      183           
  Lines             ?    18350           
  Branches          ?        0           
=========================================
  Hits              ?     4007           
  Misses            ?    14035           
  Partials          ?      308           

Flag	Coverage Δ
unittests	21.83% <0.00%> (?)

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[RainbowMango]

@ikaven1024 Could you please take a look?

[RainbowMango]

/assign @XiShanYongYe-Chang

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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[ikaven1024]

@ikaven1024 Could you please take a look?

Sorry for my late reply. I am not familiar with Codecov, and need to look into it. I will spend time leaning it.

[Poor12]

/lgtm