Migrate KNN serialization interfaces

[ajleong623]

Description

Adds knn interfaces that are shared between knn plugins https://github.com/opensearch-project/k-NN/tree/main and https://github.com/opensearch-project/opensearch-jvector/tree/main to core. This PR focuses on the interfaces relating to serialization logic.

Related Issues

#20050

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

✅ Gradle check result for fff514c: SUCCESS

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.36%. Comparing base (fc33a53) to head (fff514c).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #20513      +/-   ##
============================================
+ Coverage     73.19%   73.36%   +0.16%     
- Complexity    71975    72145     +170     
============================================
  Files          5796     5798       +2     
  Lines        329539   329654     +115     
  Branches      47465    47491      +26     
============================================
+ Hits         241220   241842     +622     
+ Misses        69005    68434     -571     
- Partials      19314    19378      +64     

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[github-actions]

❌ Gradle check result for db4eac6: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?