[Backport 2.x]Add cluster primary balance contraint for rebalancing with buffer

[alchemist51]

Backport PR: #12656
Signed-off-by: Arpit-Bandejiya abandeji@amazon.com

(cherry picked from commit 3491bcb)

Description

[Describe what this change achieves]

Related Issues

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

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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[github-actions]

Compatibility status:

Checks if related components are compatible with change 6d67137

Incompatible components

Skipped components

Compatible components

Compatible components: [https://github.com/opensearch-project/custom-codecs.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/neural-search.git, https://github.com/opensearch-project/flow-framework.git, https://github.com/opensearch-project/cross-cluster-replication.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/job-scheduler.git, https://github.com/opensearch-project/security-analytics.git, https://github.com/opensearch-project/geospatial.git, https://github.com/opensearch-project/observability.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/k-nn.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/sql.git, https://github.com/opensearch-project/alerting.git, https://github.com/opensearch-project/performance-analyzer.git]

[github-actions]

✅ Gradle check result for 990e373: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 91.83673% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 71.12%. Comparing base (0dd892c) to head (6d67137).
Report is 102 commits behind head on 2.x.

Files	Patch %	Lines
.../allocation/allocator/BalancedShardsAllocator.java	88.23%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #13014      +/-   ##
============================================
- Coverage     71.28%   71.12%   -0.16%     
- Complexity    60145    60361     +216     
============================================
  Files          4957     4990      +33     
  Lines        282799   284574    +1775     
  Branches      41409    41605     +196     
============================================
+ Hits         201591   202415     +824     
- Misses        64189    65011     +822     
- Partials      17019    17148     +129     

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[github-actions]

❕ Gradle check result for 6d67137: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.cluster.coordination.AwarenessAttributeDecommissionIT.testConcurrentDecommissionAction
      1 org.opensearch.backwards.MixedClusterClientYamlTestSuiteIT.test {p0=search.aggregation/20_terms/string profiler via global ordinals}

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.