Support SCANN index type

[congqixia]

See also milvus-io/milvus#26099
/kind improvement

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: congqixia

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[codecov]

Codecov Report

Merging #552 (a1dbddf) into master (2607d41) will increase coverage by 0.10%.
Report is 1 commits behind head on master.
The diff coverage is 93.93%.

@@            Coverage Diff             @@
##           master     #552      +/-   ##
==========================================
+ Coverage   82.91%   83.01%   +0.10%     
==========================================
  Files          39       39              
  Lines        3599     3632      +33     
==========================================
+ Hits         2984     3015      +31     
- Misses        503      504       +1     
- Partials      112      113       +1     

Files Changed	Coverage Δ
entity/index.go	100.00% <ø> (ø)
entity/indexes_search_param_gen.go	98.34% <85.71%> (-1.66%)	⬇️
entity/indexes_gen.go	100.00% <100.00%> (ø)

[yah01]

/lgtm