introduce tests to check whether workqueue metrics exist

[chaosi-zju]

What type of PR is this?

/kind failing-test

What this PR does / why we need it:

introduce tests to check whether workqueue metrics exist

Which issue(s) this PR fixes:

Fixes part of #5954

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.36%. Comparing base (43f2953) to head (b17e3dd).
Report is 2 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6003   +/-   ##
=======================================
  Coverage   48.36%   48.36%           
=======================================
  Files         666      666           
  Lines       54831    54831           
=======================================
+ Hits        26519    26521    +2     
+ Misses      26594    26592    -2     
  Partials     1718     1718           

Flag	Coverage Δ
unittests	48.36% <ø> (+<0.01%)	⬆️

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[chaosi-zju]

@RainbowMango

Note: my this PR is not fabricated, it is based on the implementation referenced from Kubernetes:

https://github.com/kubernetes/kubernetes/blob/master/test/e2e/framework/metrics/metrics_grabber.go

[chaosi-zju]

@XiShanYongYe-Chang would you also help take a look, thanks

[XiShanYongYe-Chang]

/assign