use singleton ratelimiter for dynamically created clients

[zach593]

What type of PR is this?

/kind bug

What this PR does / why we need it:

see #6094, this PR add the a ratelimiterGetter singleton for dynamically created cluster clients, to let the rate limiter to more accurately limit the total qps of multiple dynamically created clients .

Which issue(s) this PR fixes:

#6094

Special notes for your reviewer:

I found it difficult to test using mock client, because the existing fake client implementations do not accept ratelimiter parameters. However, I added some tests in pkg/util/ratelimiter_test.go to simulate and illustrate the final effect.

If we want to test the rate limit more completely, we may need to introduce envTest (a sub package of controller-runtime), but this requires more general considerations, because the impact is large, so it will not be expanded in this PR.

Does this PR introduce a user-facing change?:

karmada-controller-manager, karmada-agent, karmada-metrics-adapter: rate limit parameters of  'cluster-api-qps' and 'cluster-api-burst', these parameters will be stricter and administrators may need to adjust them to get the same effect as before the update.

[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign xishanyongye-chang for approval. For more information see the Kubernetes Code Review Process.

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Needs approval from an approver in each of these files:

• cmd/OWNERS
• pkg/controllers/OWNERS
• pkg/metricsadapter/OWNERS
• pkg/search/OWNERS
• pkg/util/OWNERS
• test/OWNERS

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[Copilot]

PR Overview

This PR implements a new rate limiting mechanism by switching from setting QPS and Burst values directly on REST configurations to using a singleton ratelimiterGetter based on the token bucket algorithm. The changes span multiple components (agent, aggregated-apiserver, metrics-adapter, scheduler, controller-manager, etc.), ensuring that dynamically created clients consistently use the new rate limiter setup.

• Replace direct QPS/Burst assignment with flowcontrol.NewTokenBucketRateLimiter.
• Update client and dynamic client setup functions to accept a ClientOption containing the new RateLimiterGetter.
• Amend tests to align with the new ClientOption structure.

Reviewed Changes

File	Description
cmd/agent/app/agent.go	Updates kubeconfig construction to use RateLimiter.
cmd/aggregated-apiserver/app/options/options.go	Switches REST config rate limiter to token bucket mechanism.
cmd/metrics-adapter/app/options/options.go	Modifies both REST config and metrics controller to use the new limiter.
cmd/scheduler-estimator/app/scheduler-estimator.go	Applies new rate limiter when building dynamic clients.
cmd/descheduler/app/descheduler.go	Similar rate limiter update for client configuration.
cmd/scheduler/app/scheduler.go	Replaces QPS/Burst assignment with rate limiter initialization.
cmd/karmada-search/app/karmada-search.go	Updates client config in search component to use the rate limiter.
cmd/controller-manager/app/controllermanager.go	Adjusts multiple client creation paths to use new ClientOption.
cmd/webhook/app/webhook.go	Refactors webhook config to adopt rate limiter setup.
pkg/metricsadapter/multiclient/client.go	Introduces nil-check logic before applying the new RateLimiterGetter.
pkg/controllers/status/cluster_status_controller_test.go	Updates test client options to remove explicit QPS/Burst values.
pkg/controllers/status/cluster_status_controller.go	Changes function signatures to pass ClientOption to dynamic client setup.
pkg/controllers/status/work_status_controller.go	Modifies dynamic client creation to include the new ClientOption.
pkg/search/controller.go	Adjusts dynamic client builder to pass nil for ClientOption where applicable.
pkg/controllers/context/context.go	Adds ClientOption to the controller context structure.
pkg/controllers/mcs/service_export_controller.go	Updates dynamic client setup to use ClientOption.
pkg/controllers/multiclusterservice/endpointslice_collect_controller.go	Ensures dynamic client creation includes ClientOption.

Copilot reviewed 26 out of 26 changed files in this pull request and generated 2 comments.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 45.45455% with 42 lines in your changes missing coverage. Please review.

Project coverage is 47.95%. Comparing base (8d43fe2) to head (410c5d4).

Files with missing lines	Patch %	Lines
pkg/util/membercluster_client.go	12.50%	10 Missing and 4 partials ⚠️
cmd/controller-manager/app/controllermanager.go	0.00%	10 Missing ⚠️
cmd/agent/app/agent.go	0.00%	6 Missing ⚠️
pkg/metricsadapter/controller.go	0.00%	3 Missing ⚠️
pkg/metricsadapter/multiclient/client.go	0.00%	3 Missing ⚠️
cmd/metrics-adapter/app/options/options.go	0.00%	2 Missing ⚠️
pkg/controllers/mcs/service_export_controller.go	0.00%	1 Missing ⚠️
...clusterservice/endpointslice_collect_controller.go	0.00%	1 Missing ⚠️
pkg/search/controller.go	0.00%	1 Missing ⚠️
pkg/util/objectwatcher/objectwatcher.go	80.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6192      +/-   ##
==========================================
- Coverage   47.97%   47.95%   -0.03%     
==========================================
  Files         674      675       +1     
  Lines       55841    55886      +45     
==========================================
+ Hits        26789    26798       +9     
- Misses      27305    27334      +29     
- Partials     1747     1754       +7     

Flag	Coverage Δ
unittests	47.95% <45.45%> (-0.03%)	⬇️

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[zach593]

/remove-kind feature
/kind bug

I think the issue with the rate limiter not working is more like a bug, please feel free to correct me if anyone thinks it should not be.