S3 Event Consistency via metadata and JSON changes

[dlvenable]

Description

This makes a few end-user changes related to the S3 source:

• Moves the key and bucket keys into a metadata key that starts with s3/ by default.
• Adds the metadata_root_key S3 source config which allows modifying the key specified above.
• Changes the JSON codec to populate the root Event rather than the message key.

Along with this change, I did some refactoring to decouple the metadata population from the S3 object processing.

Issues Resolved

Resolves #1687

Check List

• New functionality includes testing.
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

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.

[codecov-commenter]

Codecov Report

Merging #1803 (bade15d) into main (504e8b8) will decrease coverage by 0.11%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #1803      +/-   ##
============================================
- Coverage     93.96%   93.84%   -0.12%     
  Complexity     1457     1457              
============================================
  Files           188      188              
  Lines          4275     4275              
  Branches        347      347              
============================================
- Hits           4017     4012       -5     
- Misses          177      182       +5     
  Partials         81       81              

Impacted Files	Coverage Δ
.../org/opensearch/dataprepper/pipeline/Pipeline.java	88.40% <0.00%> (-4.35%)	⬇️
...rwarder/discovery/AwsCloudMapPeerListProvider.java	92.59% <0.00%> (-2.47%)	⬇️

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[oeyh]

Looks good!