fix: Fix errors in the Index service APIs are ignored (#31077)

[bigsheeper]

In Index service APIs, return error if occurs instead of always returning nil. Additionally, add more tests to cover this scenario.

issue: #31069, #31027

pr: #31077

[weiliu1031]

/lgtm

[czs007]

/approve

[sre-ci-robot]

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• internal/distributed/OWNERS [czs007]
• internal/querycoordv2/meta/OWNERS [czs007]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.21%. Comparing base (53f5a67) to head (afbe297).

Additional details and impacted files

@@            Coverage Diff             @@
##              2.3   #31086      +/-   ##
==========================================
- Coverage   82.22%   82.21%   -0.01%     
==========================================
  Files         843      843              
  Lines      122047   122063      +16     
==========================================
+ Hits       100348   100354       +6     
- Misses      18466    18475       +9     
- Partials     3233     3234       +1     

Files	Coverage Δ
internal/distributed/datacoord/client/client.go	96.96% <100.00%> (+0.05%)	⬆️
internal/querycoordv2/meta/coordinator_broker.go	93.08% <100.00%> (+0.30%)	⬆️

... and 13 files with indirect coverage changes