[Remote Store] Introducing mixed mode support for remote store migrat…

[gbbafna]

…ion (#11986)

• Introducing mixed mode support for remote store migration

• Adding changelog

• Refactoring IT and naming changes

• Missing java doc

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Description

To enable migration of document replication clusters to remote store backed clusters, we will need to allow mixed mode clusters . The behavior is going to be as followed

1. STRICT Mode - Only one type of node (remote or docrep node) is allowed to join cluster.
   

2. MIXED Mode - Any type of node (remote or docrep node) is allowed to join cluster. We will also need another DIRECTION setting to dictate which nodes the new index is going to land . MIXED Mode should only be allowed in an experimental flag till we add complete support for same.
   

Related Issues

Resolves #12245

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 ca29f40

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

[github-actions]

✅ Gradle check result for ca29f40: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 76.74419% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 71.35%. Comparing base (0dd892c) to head (ca29f40).
Report is 39 commits behind head on 2.x.

Files	Patch %	Lines
...earch/node/remotestore/RemoteStoreNodeService.java	63.63%	7 Missing and 1 partial ⚠️
...nsearch/cluster/coordination/JoinTaskExecutor.java	90.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #12751      +/-   ##
============================================
+ Coverage     71.28%   71.35%   +0.07%     
- Complexity    60145    60251     +106     
============================================
  Files          4957     4963       +6     
  Lines        282799   283303     +504     
  Branches      41409    41470      +61     
============================================
+ Hits         201591   202164     +573     
+ Misses        64189    64062     -127     
- Partials      17019    17077      +58     

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