Fix PostingsFormat in KNN Codec (#236)

[vamshin]

• postings list fix

Issue #, if available: https://github.com/opendistro-for-elasticsearch/k-NN/issues/227

Description of changes: https://github.com/opendistro-for-elasticsearch/k-NN/pull/236

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[codecov[bot]]

Codecov Report

Merging #248 into opendistro-1.10 will decrease coverage by 0.10%. The diff coverage is 100.00%.

@@                  Coverage Diff                  @@
##             opendistro-1.10     #248      +/-   ##
=====================================================
- Coverage              77.87%   77.76%   -0.11%     
- Complexity               308      311       +3     
=====================================================
  Files                     50       50              
  Lines                   1184     1192       +8     
  Branches                 100      100              
=====================================================
+ Hits                     922      927       +5     
- Misses                   218      221       +3     
  Partials                  44       44              

Impacted Files	Coverage Δ	Complexity Δ
...csearch/knn/index/codec/KNN86Codec/KNN86Codec.java	92.00% <100.00%> (+2.00%)	14.00 <4.00> (+2.00)
...roforelasticsearch/knn/plugin/KNNCodecService.java	75.00% <100.00%> (+8.33%)	3.00 <1.00> (+1.00)
...oforelasticsearch/knn/plugin/KNNEngineFactory.java	100.00% <100.00%> (ø)	3.00 <2.00> (ø)
...istroforelasticsearch/knn/index/KNNIndexCache.java	92.30% <0.00%> (-2.89%)	35.00% <0.00%> (ø%)

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[vamshin]

Manually verified suggest Field to check PostingsFormat fix

curl -X PUT "localhost:9200/music?pretty" -H 'Content-Type: application/json' -d'

{ "settings": { "index": { "knn": true } }, "mappings": { "properties": { "suggest": { "type": "completion" } } } } '

curl -X POST "localhost:9200/music/_doc/1?refresh=true" -H 'Content-Type: application/json' -d' { "suggest" : { "input": [ "Nevermind", "Nirvana" ], "weight" : 34 } } '

curl -X POST "localhost:9200/music/_search?pretty" -H 'Content-Type: application/json' -d' { "suggest": { "song-suggest": { "prefix": "nir",
"completion": {
"field": "suggest"
} } } } '

Output:-

{ "took" : 92, "timed_out" : false, "_shards" : { "total" : 1, "successful" : 1, "skipped" : 0, "failed" : 0 }, "hits" : { "total" : { "value" : 0, "relation" : "eq" }, "max_score" : null, "hits" : [ ] }, "suggest" : { "song-suggest" : [ { "text" : "nir", "offset" : 0, "length" : 3, "options" : [ { "text" : "Nirvana", "_index" : "music", "_type" : "_doc", "_id" : "1", "_score" : 34.0, "_source" : { "suggest" : { "input" : [ "Nevermind", "Nirvana" ], "weight" : 34 } } } ] } ] } }