Reuse bucket when reduce terms buckets

[bowenlan-amzn]

Description

When the requested field's cardinality is high, the reduce of term aggregation bucket creation become heavy.
Every cardinality is represented by a bucket. For each reduce, we merge the bucket of same key from multiple responses together, and create a new bucket for that.

This PR tries to reuse the existing bucket from the 1st response by in-place updating the field values, instead of creating one.

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

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 ae8b2ac: 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?

[github-actions]

❌ Gradle check result for ef07406: FAILURE

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[github-actions]

✅ Gradle check result for be081cb: SUCCESS

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.36%. Comparing base (672039d) to head (be081cb).
⚠️ Report is 93 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #20483      +/-   ##
============================================
+ Coverage     73.25%   73.36%   +0.11%     
- Complexity    71979    72053      +74     
============================================
  Files          5796     5796              
  Lines        329287   329293       +6     
  Branches      47419    47420       +1     
============================================
+ Hits         241203   241575     +372     
+ Misses        68759    68401     -358     
+ Partials      19325    19317       -8     

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[opensearch-trigger-bot]

This PR is stalled because it has been open for 30 days with no activity.