[Feature/extensions] Add contentParser method to ExtensionRestRequest

[dbwiddis]

Signed-off-by: Daniel Widdis [email protected]

Companion PR: opensearch-project/opensearch-sdk-java#192

This PR does not change the API and can be merged at any time before the companion PR even if it is still in review.

Description

Adds a contentParser() method to the ExtensionRestRequest class to enable extensions to parse REST requests with bodies containing JSON, SMILE, YAML, or CBOR.

Issues Resolved

OpenSearch part of SDK #178

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/4545/
• CommitID: c60eddf

[codecov-commenter]

Codecov Report

Merging #4760 (c60eddf) into feature/extensions (dfeefa6) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@                   Coverage Diff                    @@
##             feature/extensions    #4760      +/-   ##
========================================================
- Coverage                 70.71%   70.66%   -0.06%     
+ Complexity                57896    57884      -12     
========================================================
  Files                      4706     4706              
  Lines                    277831   277834       +3     
  Branches                  40389    40389              
========================================================
- Hits                     196481   196330     -151     
- Misses                    65114    65250     +136     
- Partials                  16236    16254      +18     

Impacted Files	Coverage Δ
...ensearch/extensions/rest/ExtensionRestRequest.java	77.61% <100.00%> (+2.61%)	⬆️
...ava/org/opensearch/action/NoSuchNodeException.java	0.00% <0.00%> (-50.00%)	⬇️
...cluster/coordination/PendingClusterStateStats.java	20.00% <0.00%> (-48.00%)	⬇️
...arch/search/aggregations/pipeline/LinearModel.java	23.07% <0.00%> (-46.16%)	⬇️
...opensearch/persistent/PersistentTasksExecutor.java	22.22% <0.00%> (-44.45%)	⬇️
...nsearch/discovery/InitializeExtensionsRequest.java	0.00% <0.00%> (-40.00%)	⬇️
.../admin/cluster/reroute/ClusterRerouteResponse.java	60.00% <0.00%> (-40.00%)	⬇️
...h/action/ingest/SimulateDocumentVerboseResult.java	60.71% <0.00%> (-39.29%)	⬇️
...luster/routing/allocation/RoutingExplanations.java	62.06% <0.00%> (-37.94%)	⬇️
...cluster/coordination/PublishClusterStateStats.java	33.33% <0.00%> (-37.51%)	⬇️
... and 482 more

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