[DOC] Add documentation for index.routing.allocation.total_primary_shards_per_node and cluster.routing.allocation.total_primary_shards_per_node

[pandeydivyansh1803]

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. Adding documentation for two important OpenSearch routing allocation settings specifically designed for remote-store enabled clusters. These settings control primary shard distribution across nodes and help prevent uneven primary shard allocation:

index.routing.allocation.total_primary_shards_per_node: Index-level setting that limits the number of primary shards per node for a specific index
cluster.routing.allocation.total_primary_shards_per_node: Cluster-level setting that sets a global limit on primary shards per node
This documentation will help users:

->Better understand primary shard allocation controls
->Implement more balanced shard distribution strategies
->Prevent node overload from excessive primary shard allocation
->Configure these settings at both index and cluster levels
->The documentation will include setting descriptions, usage examples, and best practices for primary shard allocation management.

Version: OpenSearch version 3.0.0

What other resources are available? opensearch-project/OpenSearch#17293