[Backport 2.x] Add ApiSpecFetcher for Fetching and Comparing API Specifications

[opensearch-trigger-bot]

Backport 57b8b59 from #900.

[dbwiddis]

CI failing due to Lucene 9.12 upgrade and issues with build. Follow:

• Fix lucene codec after lucene version bumped to 9.12 k-NN#2195 (once this merges we should be good to go)
• https://opensearch.slack.com/archives/C04UTNM338A/p1728341414662579 (indicates it should resolve within 24 hours)

[navneet1v]

@dbwiddis the backport should not because of lucene upgrade. As lucene upgrade has happened only for main branch. :D

[dbwiddis]

@dbwiddis the backport should not because of lucene upgrade. As lucene upgrade has happened only for main branch. :D

@navneet1v yeah, didn't spend long enough looking at the log, saw NoClassDefFoundError and just assumed.

Seems we need some more dependencies on the backport, related to slf4j (CC: @junweid62)

needs slf4j import

[dbwiddis]

Looks like on main we get slf4j.api from rest client

runtimeClasspath - Runtime classpath of source set 'main'.
+--- org.opensearch.client:opensearch-rest-client:3.0.0-SNAPSHOT
|    +--- org.apache.httpcomponents.client5:httpclient5:5.2.1
|    +--- org.apache.httpcomponents.core5:httpcore5:5.2.2 -> 5.3
|    +--- org.apache.httpcomponents.core5:httpcore5-h2:5.2.2
|    +--- commons-codec:commons-codec:1.16.1
|    +--- commons-logging:commons-logging:1.2
|    \--- org.slf4j:slf4j-api:1.7.36

but on 2.x we don't

compileClasspath - Compile classpath for source set 'main'.
+--- org.opensearch.client:opensearch-rest-client:2.18.0-SNAPSHOT
|    +--- org.apache.httpcomponents:httpclient:4.5.14
|    +--- org.apache.httpcomponents:httpcore:4.4.16
|    +--- org.apache.httpcomponents:httpasyncclient:4.1.5
|    +--- org.apache.httpcomponents:httpcore-nio:4.4.16
|    +--- commons-codec:commons-codec:1.16.1
|    +--- commons-logging:commons-logging:1.2
|    +--- io.projectreactor:reactor-core:3.5.20
|    \--- org.reactivestreams:reactive-streams:1.0.4

[codecov]

Codecov Report

Attention: Patch coverage is 84.44444% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.07%. Comparing base (0cde785) to head (d3c8141).
Report is 2 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
.../opensearch/flowframework/util/ApiSpecFetcher.java	82.05%	4 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x     #906      +/-   ##
============================================
+ Coverage     78.04%   78.07%   +0.03%     
- Complexity      977      995      +18     
============================================
  Files            97       99       +2     
  Lines          4554     4621      +67     
  Branches        423      431       +8     
============================================
+ Hits           3554     3608      +54     
- Misses          823      833      +10     
- Partials        177      180       +3     

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