[RW Separation] Disable auto-expand-replica case with search replicas

[vinaykpud]

Is your feature request related to a problem? Please describe

The setting index.auto_expand_replicas determines whether the cluster should automatically adjust the number of replica shards for an index based on the current number of data nodes. More details on this can be found here

Requirement:

• If an index is configured with index.auto_expand_replicas and does not have a search replica, any attempt to add a new search replica should be disallowed.
• If an index already has a search replica, any attempt to enable index.auto_expand_replicas should be disallowed.

Related component

Search:Performance