[Backport 2.x] Implement buildEmptyAggregations for MultiTermsAggregator (#7089)

[opensearch-trigger-bot]

Backport 86f955c from #7318.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18639/
• CommitID: 1d05e19
  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 (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18699/
• CommitID: 93d58b3
  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 (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      3 org.opensearch.remotestore.SegmentReplicationUsingRemoteStoreIT.testPressureServiceStats

• URL: https://build.ci.opensearch.org/job/gradle-check/18716/
• CommitID: 93d58b3
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #8333 (93d58b3) into 2.x (2dbe33f) will decrease coverage by 0.06%.
The diff coverage is 56.95%.

@@             Coverage Diff              @@
##                2.x    #8333      +/-   ##
============================================
- Coverage     70.54%   70.49%   -0.06%     
- Complexity    56776    56868      +92     
============================================
  Files          4706     4714       +8     
  Lines        269087   269640     +553     
  Branches      39773    39855      +82     
============================================
+ Hits         189836   190079     +243     
- Misses        62886    63237     +351     
+ Partials      16365    16324      -41     

Impacted Files	Coverage Δ
...va/org/opensearch/geometry/GeometryCollection.java	89.28% <0.00%> (-7.02%)	⬇️
...in/java/org/opensearch/wildfly/model/Employee.java	0.00% <ø> (ø)
...ildfly/transport/RestHighLevelClientActivator.java	0.00% <ø> (ø)
...transport/RestHighLevelClientEmployeeResource.java	0.00% <ø> (ø)
...wildfly/transport/RestHighLevelClientProducer.java	0.00% <ø> (ø)
...ly/transport/RestHighLevelJacksonJsonProvider.java	0.00% <ø> (ø)
...apshots/restore/RestoreSnapshotRequestBuilder.java	15.00% <0.00%> (-0.79%)	⬇️
...java/org/opensearch/index/fielddata/FieldData.java	70.48% <0.00%> (-3.11%)	⬇️
...rg/opensearch/index/translog/RemoteFsTranslog.java	69.27% <0.00%> (-3.56%)	⬇️
...dex/translog/transfer/TranslogTransferManager.java	78.45% <0.00%> (-1.33%)	⬇️
... and 30 more

... and 445 files with indirect coverage changes