[Searchable Remote Index] Create a prototype for CompositeStore combining remote and local store in tandem with the HybridDirectory

[kotwanikunal]

Is your feature request related to a problem? Please describe.
Coming in from #3719 and #3703 (comment) - the current store structure utilizes two independent stores to perform upload and download operations. These stores will eventually operate on the same set of local shards (starting with Searchable Remote Index (read and write operations), and the current architecture will not suffice.

Describe the solution you'd like

• This issue focuses on creating a prototype to understand the feasibility and the document the overlap, integration points with the new Hybrid directory setup created as a part of Create a prototype/design for a hybrid local/fetch-on-demand directory #7331

Describe alternatives you've considered

• N/A

Additional context

• Create a prototype/design for a hybrid local/fetch-on-demand directory #7331