Automated cherry pick of #5144: GroupClusters should sort by score and availableReplica count

[mszacillo]

Cherry pick of #5144 into release-1.10.

With this small change, we now sort clusters by taking their availableReplicas into account, rather than defaulting to the cluster's name. This helps spread resource usage across all clusters and would be helpful to use as part of the current v1.10 release.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 53.31%. Comparing base (a65e791) to head (ce89d21).

Files	Patch %	Lines
.../scheduler/core/spreadconstraint/group_clusters.go	0.00%	3 Missing and 1 partial ⚠️

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Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.10    #5180      +/-   ##
================================================
- Coverage         53.32%   53.31%   -0.01%     
================================================
  Files               253      253              
  Lines             20572    20575       +3     
================================================
  Hits              10969    10969              
- Misses             8877     8880       +3     
  Partials            726      726              

Flag	Coverage Δ
unittests	53.31% <0.00%> (-0.01%)	⬇️

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[whitewindmills]

/lgtm
/approve

[whitewindmills]

/assign @RainbowMango

[RainbowMango]

/approve
Thanks.

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango, whitewindmills

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