[Refactor] MediaTypeParserRegistry to MediaTypeRegistry

[nknize]

Coming out of #8826 (comment), this PR rote refactors MediaTypeParserRegistry to MediaTypeRegistry to make the class naming align with the intention of the logic. The MediaTypeRegistry is a mechanism for downstream extensions to register concrete MediaTypes thus having "Parser" in the name is unneeded.

relates #5910
relates #8110

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      2 org.opensearch.search.suggest.CompletionSuggestSearchIT.testSkipDuplicates
      1 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString_FailOpenEnabled

• URL: https://build.ci.opensearch.org/job/gradle-check/21188/
• CommitID: ba8a21b
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #8940 (ba8a21b) into main (4ad4182) will increase coverage by 0.13%.
Report is 1 commits behind head on main.
The diff coverage is 88.88%.

@@             Coverage Diff              @@
##               main    #8940      +/-   ##
============================================
+ Coverage     70.97%   71.11%   +0.13%     
- Complexity    57155    57242      +87     
============================================
  Files          4758     4758              
  Lines        269869   269869              
  Branches      39487    39487              
============================================
+ Hits         191545   191914     +369     
+ Misses        62119    61711     -408     
- Partials      16205    16244      +39     

Files Changed	Coverage Δ
...rg/opensearch/core/xcontent/MediaTypeRegistry.java	82.14% <0.00%> (ø)
.../opensearch/client/indices/CreateIndexRequest.java	77.77% <100.00%> (+1.11%)	⬆️
...g/opensearch/client/indices/PutMappingRequest.java	72.41% <100.00%> (ø)
.../opensearch/core/common/io/stream/StreamInput.java	89.62% <100.00%> (+0.97%)	⬆️
...n/java/org/opensearch/core/xcontent/MediaType.java	100.00% <100.00%> (ø)
...a/org/opensearch/common/xcontent/XContentType.java	100.00% <100.00%> (ø)
.../java/org/opensearch/rest/AbstractRestChannel.java	90.69% <100.00%> (ø)
...ava/org/opensearch/transport/TransportService.java	79.10% <100.00%> (-0.72%)	⬇️

... and 466 files with indirect coverage changes

[Yury-Fridlyand]

More breaking changes for god of breaking changes!