[FEATURE] Add models related to Remote-backed Storage

[Xtansia]

There is only a single very simple operation needing modelling:

• Restore /_remotestore/_restore: https://opensearch.org/docs/latest/opensearch/remote/#restoring-from-a-backup

It must be communicated via the model and any derivative generated clients, that this API is still currently experimental and as such may be subject to change and is not recommended for production use.

As this is a truly "missing" API, in that it does not exist in the clients yet, this will enable us to spike and experiment on generating only missing subsets of clients.