feat(worker): add metrics for asyncworker

[CharlesQQ]

What type of PR is this?
/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:
Fixes #5791

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 32.97872% with 63 lines in your changes missing coverage. Please review.

Project coverage is 44.83%. Comparing base (35b7e8f) to head (4892551).

Files with missing lines	Patch %	Lines
pkg/metrics/asyncworker.go	0.00%	26 Missing ⚠️
pkg/detector/detector.go	0.00%	9 Missing ⚠️
pkg/controllers/cluster/taint_manager.go	33.33%	4 Missing ⚠️
pkg/clusterdiscovery/clusterapi/clusterapi.go	0.00%	3 Missing ⚠️
pkg/controllers/mcs/service_export_controller.go	0.00%	3 Missing ⚠️
...clusterservice/endpointslice_collect_controller.go	0.00%	3 Missing ⚠️
...ependenciesdistributor/dependencies_distributor.go	25.00%	3 Missing ⚠️
pkg/util/worker/worker.go	75.00%	2 Missing and 1 partial ⚠️
...targetmarker/hpa_scale_target_marker_controller.go	0.00%	2 Missing ⚠️
cmd/agent/app/agent.go	0.00%	1 Missing ⚠️
... and 6 more

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5817      +/-   ##
==========================================
- Coverage   44.84%   44.83%   -0.01%     
==========================================
  Files         658      659       +1     
  Lines       53917    53955      +38     
==========================================
+ Hits        24180    24192      +12     
- Misses      28169    28195      +26     
  Partials     1568     1568              

Flag	Coverage Δ
unittests	44.83% <32.97%> (-0.01%)	⬇️

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