Do not send query/field in the correlation rule payload if they are empty

[amsiglan]

Description

The backend does not generate correlations if we send empty query string as part of rule payload. This PR filters out empty field/query from the payload

Issues Resolved

[List any issues this PR will resolve]

Check List

• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fba42a5) 31.01% compared to head (43c92e9) 31.01%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #817      +/-   ##
==========================================
- Coverage   31.01%   31.01%   -0.01%     
==========================================
  Files         151      151              
  Lines        5084     5091       +7     
  Branches      884      886       +2     
==========================================
+ Hits         1577     1579       +2     
- Misses       3317     3322       +5     
  Partials      190      190              

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[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-817-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 8c636bda6c6958e47fd081b7ac0827710c4f9871
# Push it to GitHub
git push --set-upstream origin backport/backport-817-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-817-to-2.x.