[Doc] Add documentation for .replication-metadata-index for cross-clu…

…ster-replication. (#6082) (#6163)

* [Doc] Add documentation for .replication-metadata-index for cross-cluster-replication.



* Update _tuning-your-cluster/replication-plugin/getting-started.md




* Update _tuning-your-cluster/replication-plugin/getting-started.md




* Update _tuning-your-cluster/replication-plugin/getting-started.md




* Update _tuning-your-cluster/replication-plugin/getting-started.md




* Update _tuning-your-cluster/replication-plugin/getting-started.md




* Update _tuning-your-cluster/replication-plugin/getting-started.md




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(cherry picked from commit 63afd67)

Signed-off-by: Sanjay Kumar <[email protected]>
Signed-off-by: Sanjay Kumar <[email protected]>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Naarcha-AWS <[email protected]>
Co-authored-by: Nathan Bower <[email protected]>

_tuning-your-cluster/replication-plugin/getting-started.md

@@ -237,6 +237,14 @@ curl -XGET -k -u 'admin:admin' 'https://localhost:9200/follower-01/_search?prett
   }]
 }
 ```
+### `.replication-metadata-store` index
+
+The `.replication-metadata-store` index is a persistent data store for replication-related metadata and auto-follow rules inside of a cluster. It stores the replication metadata of each index being replicated from the leader cluster to the follower cluster.
+
+After the first replication API trigger, the `.replication-metadata-store` index is created inside the follower cluster. Any updates or additions to replication jobs or rules are also updated in the index. This enables the plugin to maintain a comprehensive record of replication status and rules across clusters.
+
+ `.replication-metdata-store` is a hidden index.
+ {: .note}
 
 ## Pause and resume replication