Add script_fields context to KNNAllowlist

[VijayanB]

Description

Include script_fields context to existing supported context for knn methods like script_score. script_fields can be used to retrieve painless scripting evaluation.

Related Issues

1878

Check List

• [x] New functionality includes testing.
• [ ] New functionality has been documented.
• [ ] API changes companion pull request created.
• [x] 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. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[vibrantvarun]

Can you reformat PR description? Just trying to understand why we are making this change

[VijayanB]

Can you reformat PR description? Just trying to understand why we are making this change

Updated description, for background please check linked github issue on why this PR is added

[opensearch-trigger-bot[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-1917-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 75ec1268ef0a824ce8fd43dfd47851293909cd40
# Push it to GitHub
git push --set-upstream origin backport/backport-1917-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-1917-to-2.x.

[opensearch-trigger-bot[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-1917-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 75ec1268ef0a824ce8fd43dfd47851293909cd40
# Push it to GitHub
git push --set-upstream origin backport/backport-1917-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-1917-to-2.x.