Align federated GitRepository's observedGeneration semantics with its native

[yike21]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Part of #4870

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:
NONE

`karmada-controller-manager`: Mark `.status.observedGeneration` of GitRepository with `.metadata.generation` only when all members' statuses are algined with its resource template generation.

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@@            Coverage Diff            @@
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[yike21]

Use karmadactl interpret to view test results:

## Execute the statusAggregation rule
$ karmadactl interpret -f customizations.yaml --operation aggregateStatus --desired-file testdata/desired-gitrepository.yaml  --status-file testdata/status-file.yaml 
---
# [1/1] aggregatedStatus:
apiVersion: source.toolkit.fluxcd.io/v1
kind: GitRepository
metadata:
    generation: 1
    name: sample
    namespace: test-gitrepository
spec:
    interval: 30s
    ref:
        branch: master
    url: https://github.com/stefanprodan/podinfo
status:
    artifact:
        digest: sha256:a375b2ca68275734e3850d3c80e0bc20c1d7a4daa1a9717056d5c0c563ea0719
        lastUpdateTime: "2023-05-01T10:17:08Z"
        path: gitrepository/test-gitrepository/sample/0647aea75b85755411b007a290b9321668370be5.tar.gz
        revision: master@sha1:0647aea75b85755411b007a290b9321668370be5
        size: 83516
        url: http://source-controller.flux-system.svc.cluster.local./gitrepository/test-gitrepository/sample/0647aea75b85755411b007a290b9321668370be5.tar.gz
    conditions:
        - lastTransitionTime: "2023-05-01T10:17:09Z"
          message: member1=stored artifact for revision 'master@sha1:0647aea75b85755411b007a290b9321668370be5', member3=stored artifact for revision 'master@sha1:0647aea75b85755411b007a290b9321668370be5'
          observedGeneration: 1
          reason: Succeeded
          status: "True"
          type: Ready
        - lastTransitionTime: "2023-05-01T10:17:09Z"
          message: member1=stored artifact for revision 'master@sha1:0647aea75b85755411b007a290b9321668370be5', member3=stored artifact for revision 'master@sha1:0647aea75b85755411b007a290b9321668370be5'
          observedGeneration: 1
          reason: Succeeded
          status: "True"
          type: ArtifactInStorage
    observedGeneration: 1

## Execute the statusReflection rule
$ karmadactl interpret -f customizations.yaml --operation interpretStatus --observed-file testdata/observed-gitrepository.yaml 
---
# [1/1] status:
artifact:
    digest: sha256:a375b2ca68275734e3850d3c80e0bc20c1d7a4daa1a9717056d5c0c563ea0719
    lastUpdateTime: "2023-05-01T10:17:09Z"
    path: gitrepository/test-gitrepository/sample/0647aea75b85755411b007a290b9321668370be5.tar.gz
    revision: master@sha1:0647aea75b85755411b007a290b9321668370be5
    size: 83516
    url: http://source-controller.flux-system.svc.cluster.local./gitrepository/test-gitrepository/sample/0647aea75b85755411b007a290b9321668370be5.tar.gz
conditions:
    - lastTransitionTime: "2023-05-01T10:17:09Z"
      message: stored artifact for revision 'master@sha1:0647aea75b85755411b007a290b9321668370be5'
      observedGeneration: 1
      reason: Succeeded
      status: "True"
      type: Ready
    - lastTransitionTime: "2023-05-01T10:17:09Z"
      message: stored artifact for revision 'master@sha1:0647aea75b85755411b007a290b9321668370be5'
      observedGeneration: 1
      reason: Succeeded
      status: "True"
      type: ArtifactInStorage
generation: 1
observedGeneration: 1
resourceTemplateGeneration: 1

[XiShanYongYe-Chang]

Hi @veophi, can you help take a review?
cc @veophi

[veophi]

/lgtm

[karmada-bot]

@veophi: changing LGTM is restricted to collaborators

In response to this:

/lgtm

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[RainbowMango]

/lgtm
/approve

Thanks.

[karmada-bot]

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