fix: return error if searching against BM25 output field with incorrect metric type

[zhengbuqian]

issue: #36835

currently searching BM25 output field using IP will end up in an error in segcore which is hard to understand. now returning error in query node delegator and provide more useful error message

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Please upload report for BASE (master@72dc07b). Learn more about missing BASE report.
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/proxy/task_index.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #36910   +/-   ##
=========================================
  Coverage          ?   81.52%           
=========================================
  Files             ?     1308           
  Lines             ?   156236           
  Branches          ?        0           
=========================================
  Hits              ?   127371           
  Misses            ?    23754           
  Partials          ?     5111           

Files with missing lines	Coverage Δ
internal/querynodev2/delegator/delegator.go	87.14% <100.00%> (ø)
internal/proxy/task_index.go	80.53% <0.00%> (ø)

[aoiasd]

/lgtm

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• internal/proxy/OWNERS [czs007]
• internal/querynodev2/delegator/OWNERS [czs007]

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