[Searchable Snapshot] [Spike] Shard allocation for searchable snapshots

[kotwanikunal]

Is your feature request related to a problem? Please describe. The feature is a part of searchable snapshots tracked here - #2919 The restored snapshot will have shards which can be remotely located but allocated to the nodes with a RemoteSearcher role assigned.

Describe the solution you'd like As a part of this task, we need to

• Understand the current allocation mechanisms and logic behind shard allocation
• Understand the mechanisms involved within UltraWarm for shard allocation
• Breakdown the allocation requirements for Searchable Snapshots into necessary features and optimization buckets for further prioritization

This task will be followed with design and implementation phases from the above outcomes.

Describe alternatives you've considered N/A

Additional context #2919