Enhance FlushAll/GetFlushAllState API

[wayblink]

issue: #26777

[mergify]

@wayblink Thanks for your contribution. Please submit with DCO, see the contributing guide https://github.com/milvus-io/milvus/blob/master/CONTRIBUTING.md#developer-certificate-of-origin-dco.

[mergify]

@wayblink Please associate the related issue to the body of your Pull Request. (eg. “issue: #”)

[codecov]

Codecov Report

Merging #26802 (5e37dd0) into master (73f4347) will decrease coverage by 0.01%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #26802      +/-   ##
==========================================
- Coverage   82.30%   82.29%   -0.01%     
==========================================
  Files         796      796              
  Lines      110538   110558      +20     
==========================================
+ Hits        90973    90985      +12     
- Misses      16437    16440       +3     
- Partials     3128     3133       +5     

Files Changed	Coverage Δ
internal/datacoord/services.go	85.20% <100.00%> (+0.09%)	⬆️
internal/proxy/impl.go	85.70% <100.00%> (+0.03%)	⬆️

... and 16 files with indirect coverage changes

[mergify]

@wayblink ut workflow job failed, comment rerun ut can trigger the job again.

[bigsheeper]

/lgtm

[czs007]

/approve

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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