[Backport 2.x] Allow changing number of replicas of searchable snapshot index

[andrross]

Backports c4e703f from #11317 to 2.x

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 f12db1a

Incompatible components

Skipped components

Compatible components

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

[github-actions]

❌ Gradle check result for f12db1a: 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?

[andrross]

❌ Gradle check result for f12db1a: FAILURE

#2775

[github-actions]

❌ Gradle check result for f12db1a: 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?

[andrross]

❌ Gradle check result for f12db1a: FAILURE

#10006

[github-actions]

✅ Gradle check result for f12db1a: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c1c6494) 71.09% compared to head (f12db1a) 71.10%.
Report is 3 commits behind head on 2.x.

Additional details and impacted files

@@            Coverage Diff            @@
##                2.x   #11376   +/-   ##
=========================================
  Coverage     71.09%   71.10%           
- Complexity    59140    59223   +83     
=========================================
  Files          4869     4869           
  Lines        278725   278725           
  Branches      40847    40847           
=========================================
+ Hits         198164   198176   +12     
- Misses        63761    63818   +57     
+ Partials      16800    16731   -69     

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