enhance: [Cherry-pick] Shuffle candidates before channel assignment (#30066)

[congqixia]

Cherry-pick from master
pr: #30066

Shuffle candidates to reduce scenario that some channel allocated into same node

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9f6a19c) 82.18% compared to head (bfb5c6c) 82.20%.
Report is 9 commits behind head on 2.3.

Additional details and impacted files

@@            Coverage Diff             @@
##              2.3   #30089      +/-   ##
==========================================
+ Coverage   82.18%   82.20%   +0.01%     
==========================================
  Files         825      834       +9     
  Lines      120336   120396      +60     
==========================================
+ Hits        98901    98972      +71     
+ Misses      18207    18199       -8     
+ Partials     3228     3225       -3     

Files	Coverage Δ
internal/distributed/proxy/httpserver/utils.go	85.61% <100.00%> (+0.82%)	⬆️
...al/querycoordv2/balance/rowcount_based_balancer.go	97.63% <100.00%> (+<0.01%)	⬆️

... and 165 files with indirect coverage changes

[yah01]

/lgtm