Pin plural name for all APIs to avoid unexpected change

[RainbowMango]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:
When the controller-tools generate the CRDs, it guesses the plural name by github.com/gobuffalo/flect if the plural name is not explicitly specified.

But the rule of generating plural names might change over different github.com/gobuffalo/flect versions. See kubernetes-sigs/controller-tools#804 (comment) for an example.

So, this PR pin plural name for all APIs to avoid this unexpected change.
(We don't depend on github.com/gobuffalo/flect, but the controller-tools reply on it. We might update controller-tools.)
Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

I'm trying to update the controller-tools but found the plural name of Karmada operator changed unexpectedly(see the fix at #4777), that reminds me we'd better pin the plural name.

Does this PR introduce a user-facing change?:

NONE

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.78%. Comparing base (4e25482) to head (32a4076).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4778      +/-   ##
==========================================
- Coverage   51.78%   51.78%   -0.01%     
==========================================
  Files         250      250              
  Lines       24989    24989              
==========================================
- Hits        12941    12940       -1     
- Misses      11339    11340       +1     
  Partials      709      709              

Flag	Coverage Δ
unittests	51.78% <ø> (-0.01%)	⬇️

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[XiShanYongYe-Chang]

Thanks a lot~
/lgtm

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