fix: Search may return less result after qn recover (#36549)

[weiliu1031]

issue: #36293 #36242
pr: #36549
after qn recover, delegator may be loaded in new node, after all segment has been loaded, delegator becomes serviceable. but delegator's target version hasn't been synced, and if search/query comes, delegator will use wrong target version to filter out a empty segment list, which caused empty search result.

This pr will block delegator's serviceable status until target version is synced

---

[mergify]

@weiliu1031 E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: czs007, weiliu1031

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[codecov]

Codecov Report

Attention: Patch coverage is 89.79592% with 10 lines in your changes missing coverage. Please review.

Project coverage is 80.59%. Comparing base (074f8ee) to head (bf962a0).
Report is 2 commits behind head on 2.4.

Files with missing lines	Patch %	Lines
internal/querycoordv2/observers/target_observer.go	73.68%	6 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              2.4   #37610      +/-   ##
==========================================
- Coverage   80.60%   80.59%   -0.01%     
==========================================
  Files        1069     1069              
  Lines      166736   166731       -5     
==========================================
- Hits       134392   134374      -18     
- Misses      27935    27947      +12     
- Partials     4409     4410       +1     

Files with missing lines	Coverage Δ
internal/querycoordv2/dist/dist_controller.go	85.71% <100.00%> (+0.29%)	⬆️
internal/querycoordv2/dist/dist_handler.go	95.79% <100.00%> (+0.43%)	⬆️
internal/querycoordv2/meta/leader_view_manager.go	95.88% <100.00%> (+0.02%)	⬆️
internal/querycoordv2/meta/target_manager.go	90.19% <100.00%> (-0.05%)	⬇️
internal/querycoordv2/server.go	81.97% <100.00%> (+0.13%)	⬆️
internal/querycoordv2/services.go	85.26% <ø> (ø)
internal/querycoordv2/utils/util.go	82.31% <100.00%> (ø)
internal/querycoordv2/observers/target_observer.go	87.07% <73.68%> (+5.99%)	⬆️

... and 25 files with indirect coverage changes