Support of new k-NN query parameter, expand_nested

[bzhangam]

Description

Support new knn query parameter expand_nested_docs.

Related Issues

Resolves #1008

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[yizheliu-amazon]

LGTM overall

[heemin32]

Please resolve the changelog conflict

[heemin32]

1. Remove [FEATURE] from PR title.
2. Keep the CHANGELOG entry to be same as PR title.

[martin-gaievski]

Overall code looks good to me.
One additional point - I think we have reached the point of NeuralQueryBuild having that always growing constructor of gazillion fields. Can you please add a builder class similar to one in KNNQueryBuilder, or log a new issue for this repo if the effort is beyond your bandwidth?

[bzhangam]

Overall code looks good to me. One additional point - I think we have reached the point of NeuralQueryBuild having that always growing constructor of gazillion fields. Can you please add a builder class similar to one in KNNQueryBuilder, or log a new issue for this repo if the effort is beyond your bandwidth?

I'd like to create a new issue for it. - #1025

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.72%. Comparing base (3d72cc3) to head (fa149d4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1013      +/-   ##
============================================
+ Coverage     78.55%   78.72%   +0.16%     
- Complexity     1028     1033       +5     
============================================
  Files            85       85              
  Lines          3623     3633      +10     
  Branches        605      609       +4     
============================================
+ Hits           2846     2860      +14     
+ Misses          528      525       -3     
+ Partials        249      248       -1     

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[martin-gaievski]

Looks good, thank you

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-1013-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 fba4961e9ec5fe28dabb3b004a1ea82b30d45773
# Push it to GitHub
git push --set-upstream origin backport/backport-1013-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-1013-to-2.x.