Add a sync option to federated shares

Is your feature request related to a problem? Please describe.
It is not relied to a problem. I was looking for a way other than scripting to sync photos between servers ( backups ) and i've tried using your federated share feature. I though that it would sync from one server to another but i was wrong. It may not be the case but adding it as optional feature could be interesting for users. Server administrator could prevent this action.

Describe the solution you'd like
I don't know what would be the implementation on the backend.

For the user sharing : there could be a "syncable" toggle that permit/prevent the user receiving the share to sync

For the user receiving the share : a folder option to "sync" and "keep in sync"

• one sync the current state
• the other one keep syncing with the remote state

For the administrator :

• a toggle to permit/prevent share sync

Describe alternatives you've considered
I have considered making client side scripts on my friend server. It's not a problem, just a feature that could be useful for less tech-align users. I've searched for apps to do so and there was none, but I think it could be a great "base" feature

The issue names no files, tests, or entry points. Start by investigating the existing federated-share flows for the sharing user, recipient, and administrator. Define the scope and behavior for one-time sync, continuous sync, and administrator permission before identifying the affected code and tests.