Approve re-sharing of shares with other users or groups

[!TIP]

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Is your feature request related to a problem? Please describe.

When a user reshares content of your shared directory its not clearly visible in larger directories. Resharing of files can cause dangerous data leaks. This is especially important for sensitive files, where resharing needs to be explicitly controlled (e.g. finances, hr).

Describe the solution you'd like

Provide a way for approval when a user requests to reshare content of your shared directory or implement better ways to keep an overview of resharing.

Describe alternatives you've considered

Globally disabling resharing or selectively on the directory is not desired. It's fine to reshare, just needs a way to control it.

Additional context

The issue names Nextcloud's Sharing app but no files, tests, or entry points. Begin by tracing the existing resharing permission flow and clarify the approval model with maintainers before implementation. Done should be a testable way to control resharing of shared-directory content without globally disabling resharing.