Add MultiClusterService FeatureGate

[XiShanYongYe-Chang]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Add MultiClusterService FeatureGate to allow users to decide whether to enable MultiClusterService functionality.

Which issue(s) this PR fixes:
Part of #4294

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Introduced `MultiClusterService` feature gate which now defaults to `alpha`.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (68d937e) 51.79% compared to head (40da94f) 51.79%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4347      +/-   ##
==========================================
- Coverage   51.79%   51.79%   -0.01%     
==========================================
  Files         243      243              
  Lines       24112    24112              
==========================================
- Hits        12490    12488       -2     
- Misses      10942    10944       +2     
  Partials      680      680              

Flag	Coverage Δ
unittests	51.79% <ø> (-0.01%)	⬇️

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[XiShanYongYe-Chang]

When I set MultiClusterService featuregate to false in the karmada-controller-manager and karmada-agent, it will not start the related controller.

I1130 14:46:17.557263       1 controllermanager.go:136] karmada-controller-manager version: version.Info{GitVersion:"v1.8.0-preview2-41-g1ddc2c2c6-dirty", GitCommit:"1ddc2c2c668caf9bc3cbf1a40c7417f74090dba8", GitTreeState:"dirty", BuildDate:"2023-11-30T14:23:56Z", GoVersion:"go1.20.4", Compiler:"gc", Platform:"linux/amd64"}
I1130 14:46:17.592451       1 reflector.go:287] Starting reflector *v1.Service (0s) from k8s.io/client-go/informers/factory.go:150
I1130 14:46:17.592475       1 reflector.go:323] Listing and watching *v1.Service from k8s.io/client-go/informers/factory.go:150
I1130 14:46:17.693090       1 shared_informer.go:341] caches populated
I1130 14:46:17.693220       1 context.go:160] Starting "workStatus"
I1130 14:46:17.693311       1 context.go:170] Started "workStatus"
I1130 14:46:17.693323       1 context.go:160] Starting "serviceExport"
I1130 14:46:17.693383       1 context.go:170] Started "serviceExport"
I1130 14:46:17.693396       1 context.go:160] Starting "endpointSlice"
I1130 14:46:17.693405       1 context.go:170] Started "endpointSlice"
I1130 14:46:17.693411       1 context.go:160] Starting "federatedResourceQuotaStatus"
I1130 14:46:17.693440       1 context.go:170] Started "federatedResourceQuotaStatus"
I1130 14:46:17.693447       1 context.go:160] Starting "cluster"
I1130 14:46:17.693601       1 context.go:170] Started "cluster"
I1130 14:46:17.693617       1 context.go:160] Starting "clusterStatus"
I1130 14:46:17.693783       1 context.go:170] Started "clusterStatus"
I1130 14:46:17.693793       1 context.go:160] Starting "serviceImport"
I1130 14:46:17.693811       1 context.go:170] Started "serviceImport"
I1130 14:46:17.693823       1 context.go:160] Starting "federatedResourceQuotaSync"
I1130 14:46:17.693841       1 context.go:170] Started "federatedResourceQuotaSync"
I1130 14:46:17.693854       1 context.go:160] Starting "cronFederatedHorizontalPodAutoscaler"
I1130 14:46:17.693866       1 context.go:170] Started "cronFederatedHorizontalPodAutoscaler"
I1130 14:46:17.693875       1 context.go:160] Starting "binding"
I1130 14:46:17.693902       1 context.go:170] Started "binding"
I1130 14:46:17.693913       1 context.go:160] Starting "namespace"
I1130 14:46:17.693928       1 context.go:170] Started "namespace"
I1130 14:46:17.693937       1 context.go:160] Starting "gracefulEviction"
I1130 14:46:17.693958       1 context.go:170] Started "gracefulEviction"
I1130 14:46:17.693970       1 context.go:160] Starting "applicationFailover"
I1130 14:46:17.693999       1 context.go:170] Started "applicationFailover"
I1130 14:46:17.694007       1 context.go:160] Starting "federatedHorizontalPodAutoscaler"
I1130 14:46:17.694067       1 context.go:170] Started "federatedHorizontalPodAutoscaler"
I1130 14:46:17.694076       1 context.go:160] Starting "execution"
I1130 14:46:17.694095       1 context.go:170] Started "execution"
I1130 14:46:17.694102       1 context.go:160] Starting "unifiedAuth"
I1130 14:46:17.694115       1 context.go:170] Started "unifiedAuth"
I1130 14:46:17.694120       1 context.go:160] Starting "bindingStatus"
I1130 14:46:17.694153       1 context.go:170] Started "bindingStatus"
I1130 14:46:17.694165       1 context.go:160] Starting "hpaReplicasSyncer"
I1130 14:46:17.694244       1 context.go:170] Started "hpaReplicasSyncer"
I1130 14:46:17.694334       1 reflector.go:287] Starting reflector *v1alpha2.ClusterResourceBinding (0s) from sigs.k8s.io/controller-runtime/pkg/cache/internal/informers.go:233

I1130 14:34:51.274461       1 agent.go:139] karmada-agent version: version.Info{GitVersion:"v1.8.0-preview2-41-g1ddc2c2c6-dirty", GitCommit:"1ddc2c2c668caf9bc3cbf1a40c7417f74090dba8", GitTreeState:"dirty", BuildDate:"2023-11-30T14:25:13Z", GoVersion:"go1.20.4", Compiler:"gc", Platform:"linux/amd64"}
I1130 14:34:55.477352       1 reflector.go:287] Starting reflector *v1.Service (0s) from k8s.io/client-go/informers/factory.go:150
I1130 14:34:55.477441       1 reflector.go:323] Listing and watching *v1.Service from k8s.io/client-go/informers/factory.go:150
I1130 14:34:55.577465       1 shared_informer.go:341] caches populated
I1130 14:34:55.577566       1 context.go:160] Starting "execution"
I1130 14:34:55.577637       1 context.go:170] Started "execution"
I1130 14:34:55.577656       1 context.go:160] Starting "workStatus"
I1130 14:34:55.577829       1 context.go:170] Started "workStatus"
I1130 14:34:55.577843       1 context.go:160] Starting "serviceExport"
I1130 14:34:55.577912       1 context.go:170] Started "serviceExport"
W1130 14:34:55.577924       1 context.go:157] "certRotation" is disabled
I1130 14:34:55.577930       1 context.go:160] Starting "clusterStatus"
I1130 14:34:55.578176       1 context.go:170] Started "clusterStatus"
I1130 14:34:55.578240       1 shared_informer.go:341] caches populated
I1130 14:34:55.578320       1 leaderelection.go:245] attempting to acquire leader lease karmada-system/karmada-agent-member3...
I1130 14:34:55.591439       1 leaderelection.go:255] successfully acquired lease karmada-system/karmada-agent-member3

[jwcesign]

/lgtm

[RainbowMango]

/approve

[karmada-bot]

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This pull-request has been approved by: RainbowMango

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