#2178 Using elkan K-Means to improve IVF

[shengjun1985]

Signed-off-by: shengjun.li shengjun.li@zilliz.com

What type of PR is this?
feature

What this PR does / why we need it:
Using elkan K-Means to improve IVF

Which issue(s) this PR fixes:
#2178

Special notes for your reviewer:
no

Does this PR introduce a user-facing change?:
no

Additional documentation (e.g. design docs, usage docs, etc.):
none

[codecov]

Codecov Report

Merging #2180 into master will increase coverage by 1.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2180      +/-   ##
==========================================
+ Coverage   89.04%   90.06%   +1.01%     
==========================================
  Files         375      410      +35     
  Lines       22838    25091    +2253     
==========================================
+ Hits        20336    22598    +2262     
+ Misses       2502     2493       -9     

Impacted Files	Coverage Δ
.../knowhere/knowhere/index/vector_index/IndexNSG.cpp	92.75% <0.00%> (-4.03%)	⬇️
...src/server/delivery/request/CreateIndexRequest.cpp	89.36% <0.00%> (-2.95%)	⬇️
core/src/storage/disk/DiskOperation.cpp	29.41% <0.00%> (-1.84%)	⬇️
core/src/server/delivery/request/SearchRequest.cpp	67.69% <0.00%> (-0.97%)	⬇️
...nowhere/knowhere/index/vector_index/IndexAnnoy.cpp	75.60% <0.00%> (-0.30%)	⬇️
core/src/server/grpc_impl/GrpcRequestHandler.cpp	68.56% <0.00%> (-0.08%)	⬇️
core/src/db/meta/SqliteMetaImpl.cpp	91.42% <0.00%> (-0.05%)	⬇️
core/src/db/DBImpl.cpp	84.01% <0.00%> (-0.02%)	⬇️
core/unittest/db/test_db_mysql.cpp	99.63% <0.00%> (-0.01%)	⬇️
core/src/cache/LRU.h	100.00% <0.00%> (ø)
... and 112 more

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏