[RW Separation] Search replica need to be counted for allocation awareness balance

[vinaykpud]

Is your feature request related to a problem? Please describe

Currently following settings used to enforce an even distribution of shards across all zones and avoid hotspots.

PUT _cluster/settings
{
  "persistent": {
    "cluster": {
      "routing.allocation.awareness.balance": "true"
    }
  }
}

If this settings is set as true, the total number of shards for the index must be a multiple of the highest count for any awareness attribute. Currently search replica count is not taken account. If this setting is enabled we need to ensure if search replicas can be evenly distributed.
Count of search replicas should be multiple of count of awareness attribute. ie of awareness attribute is zone, if we have 3 zones, search replicas should be multiple of 3.

Related component

Search:Performance

Describe alternatives you've considered

No response

Additional context

No response

[vinaykpud]

This is related to Meta issue : #15306