[DOC] Add documentation for cluster routing allocation settings

[Poojita-Raj]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request and all versions that are affected.

Reference: https://opensearch.org/docs/latest/api-reference/cluster-api/cluster-settings/ - This is the doc that has information about other cluster routing allocation settings.
Currently, the documentation for opensearch does not have any information on these 2 settings:

1. cluster.routing.allocation.move.primary_first - This is now deprecated. Boolean setting.
2. cluster.routing.allocation.shard_movement_strategy - This is the replacement setting for the above setting being introduced in 2.10. Enum setting can take 3 values - primary_first, replica_first and no_preference.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
Reference for (1):

• Relocate primary shards first while excluding set of nodes OpenSearch#1349
• Prioritize primary shard movement during shard relocation OpenSearch#1445

Reference for (2):

• [Segment Replication] Prioritize replica shard movement during shard relocation OpenSearch#8265
• [Segment Replication] Prioritize replica shard movement during shard relocation OpenSearch#8875
• Fix testClusterRelocationNoPreferenceShardMovementPrimaryFirstEnabled failure due to timeout OpenSearch#9420

[hdhalter]

See also opensearch-project/OpenSearch#3881 for more information.

[hdhalter]

@Poojita-Raj - we don't have a documentation resource available to work on this. Can you please create a PR with the updates?