Increase .metadata.generation once desired state of the Cluster object is changed.

[XiShanYongYe-Chang]

What type of PR is this?

/kind feature

What this PR does / why we need it:

We should set the generation field of the Cluster object. When the spec part of the Cluster object changes, the generation value should increase. Its value begins with 1.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Do we need to pay attention to the changes in labels and annotations of the Cluster object?

Does this PR introduce a user-facing change?:

`karmada-aggregated-apiserver`: Increase `.metadata.generation` once desired state of the `Cluster` object is changed.

[codecov-commenter]

Codecov Report

Merging #3241 (a4753cd) into master (fa0791e) will increase coverage by 0.05%.
The diff coverage is 93.33%.

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@@            Coverage Diff             @@
##           master    #3241      +/-   ##
==========================================
+ Coverage   49.15%   49.20%   +0.05%     
==========================================
  Files         206      206              
  Lines       18377    18388      +11     
==========================================
+ Hits         9033     9048      +15     
+ Misses       8856     8853       -3     
+ Partials      488      487       -1     

Flag	Coverage Δ
unittests	49.20% <93.33%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/scheduler/event_handler.go	26.15% <0.00%> (ø)
pkg/registry/cluster/strategy.go	61.33% <100.00%> (+6.64%)	⬆️
pkg/search/proxy/store/util.go	93.83% <0.00%> (+0.47%)	⬆️
pkg/search/proxy/store/store.go	68.42% <0.00%> (+3.15%)	⬆️

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[RainbowMango]

@Garrybest @chaunceyjiang Do you have any other comments?

Add generation filed for Cluster object.

You are not adding a field to Cluster.

[RainbowMango]

@XiShanYongYe-Chang Have you tested it? Please share a test report here.

[chaunceyjiang]

@Garrybest @chaunceyjiang Do you have any other comments?

No, LGTM

[XiShanYongYe-Chang]

Before update:

apiVersion: cluster.karmada.io/v1alpha1
kind: Cluster
metadata:
  creationTimestamp: "2023-03-06T12:24:41Z"
  finalizers:
  - karmada.io/cluster-controller
  generation: 5
  name: member1
  resourceVersion: "804"
  uid: c2b697d0-d9cc-4e32-982b-eb7c3f50082d
spec:
  apiEndpoint: https://172.18.0.4:6443
  id: 668b5146-f8f3-4592-847a-a79c34106193
  impersonatorSecretRef:
    name: member1-impersonator
    namespace: karmada-cluster
  ...

When I update the cluster apiEndpoint field, after:

apiVersion: cluster.karmada.io/v1alpha1
kind: Cluster
metadata:
  creationTimestamp: "2023-03-06T12:24:41Z"
  finalizers:
  - karmada.io/cluster-controller
  generation: 6
  name: member1
  resourceVersion: "844527"
  uid: c2b697d0-d9cc-4e32-982b-eb7c3f50082d
spec:
  apiEndpoint: https://172.18.0.4:6444
  id: 668b5146-f8f3-4592-847a-a79c34106193
  impersonatorSecretRef:
    name: member1-impersonator
    namespace: karmada-cluster
  ...

[RainbowMango]

/lgtm
/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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