Add KendraRankingResponseProcessor

[mingshl]

Description

Add a KendraRankingResponseProcessor to enable creating a pipeline using kendra-ranking:

In this PR, users can create a pipeline with kendra-ranking response processor, and use the pipeline for searching:

sample command:

1. uploading documents:

curl -XPUT localhost:9200/test1/_doc/1 -d '{
  "message": "[123:1:0309/123054.737343412:ERROR:child_process_sandbox_support_impl_linux.cc(23)] FontService unique font name matching request did not receive a response.",
  "fileset": {
    "name": "syslog"
  },
  "process": {
    "name": "org.gnome.Shell.desktop",
    "pid": 1544
  },
  "@timestamp": "2020-03-09T18:00:54.000+05:30",
  "host": {
    "hostname": "bionic",
    "name": "bionic"
  }
}'  -H "Content-Type:Application/json"

2. creating a new pipeline named test-kendra

curl -XPUT 'localhost:9200/_search/pipeline/test-kendra' --data '
{
  "description": "A pipeline to apply kendra ranking",
  "response_processors" : [
    {
      "kendra_ranking": {
        "title_field": "fileset",
        "body_field": "message",
        "doc_limit": 500
      }
    }
  ]
}' -H 'Content-Type: application/json' 

3. searching with the new pipeline test-kendra with normal query, for example match query:

curl -XGET 'localhost:9200/test1/_search?search_pipeline=test-kendra' --data '{
  "query": {
    "match": {
      "body_field": "2020-03-09T18:00:54.000+05:30"
    }
  }
' -H 'Content-Type: application/json' 

4. Expecting a response with re-rank outcomes.

Issues Resolved

#7158

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed as per the DCO using --signoff

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[codecov]

Codecov Report

Merging #137 (c1e4a0d) into main (23b5226) will increase coverage by 0.49%.
The diff coverage is 64.70%.

@@             Coverage Diff              @@
##               main     #137      +/-   ##
============================================
+ Coverage     82.05%   82.54%   +0.49%     
- Complexity      293      303      +10     
============================================
  Files            41       42       +1     
  Lines          1131     1180      +49     
  Branches        139      143       +4     
============================================
+ Hits            928      974      +46     
- Misses          127      130       +3     
  Partials         76       76              

Impacted Files	Coverage Δ
...search/search/relevance/SearchRelevancePlugin.java	0.00% <0.00%> (ø)
...nking/pipeline/KendraRankingResponseProcessor.java	89.79% <89.79%> (ø)

... and 1 file with indirect coverage changes