[Backport 1.x] [BUG FIX] Fix knn index shard to get bwc engine paths

[opensearch-trigger-bot]

Backport bb28393 from #309

[codecov-commenter]

Codecov Report

Merging #310 (bb28393) into 1.x (60766a4) will increase coverage by 0.10%.
The diff coverage is 82.55%.

❗ Current head bb28393 differs from pull request most recent head 2108ea4. Consider uploading reports for the commit 2108ea4 to get more accurate results

@@             Coverage Diff              @@
##                1.x     #310      +/-   ##
============================================
+ Coverage     83.38%   83.49%   +0.10%     
- Complexity      885      889       +4     
============================================
  Files           127      127              
  Lines          3834     3829       -5     
  Branches        361      361              
============================================
  Hits           3197     3197              
+ Misses          475      470       -5     
  Partials        162      162              

Impacted Files	Coverage Δ
...ensearch/knn/plugin/transport/GetModelRequest.java	100.00% <ø> (ø)
...rc/main/java/org/opensearch/knn/indices/Model.java	83.92% <42.85%> (+1.16%)	⬆️
...main/java/org/opensearch/knn/indices/ModelDao.java	83.64% <79.36%> (+2.05%)	⬆️
...org/opensearch/knn/index/KNNVectorFieldMapper.java	83.18% <81.94%> (-0.43%)	⬇️
.../main/java/org/opensearch/knn/index/IndexUtil.java	56.66% <100.00%> (ø)
...n/java/org/opensearch/knn/index/KNNIndexShard.java	93.75% <100.00%> (+0.72%)	⬆️
.../main/java/org/opensearch/knn/index/KNNWeight.java	75.34% <100.00%> (ø)
.../opensearch/knn/index/codec/util/KNNCodecUtil.java	94.44% <100.00%> (+0.69%)	⬆️
...arch/knn/plugin/transport/DeleteModelResponse.java	100.00% <100.00%> (ø)
... and 2 more

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[github-actions]

The backport to 1.2 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-1.2 1.2
# Navigate to the new working tree
cd .worktrees/backport-1.2
# Create a new branch
git switch --create backport-310-to-1.2
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 54d974cda4f8e86d6ef993d7702b08f1f00338a3
# Push it to GitHub
git push --set-upstream origin backport-310-to-1.2
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.2

Then, create a pull request where the base branch is 1.2 and the compare/head branch is backport-310-to-1.2.