TYPO3 Core

The fix for uniqueInSite handling and the resulting troubles
showed some limitations in flexibiltiy regarding URL generation when records are stored in a global folder.

The issue here is, that one cannot know in which site a record, that is stored anywhere, is eventually rendered and URLs are generated/resolved for.

Therefore we cannot:

1. Know based on which site(s) de-dulpication needst to be performed on
2. Know which total URLs this slug will finally have and thus cannot add a preview for editors

One idea to address that would be to evaluate TSConfig on the record storage, which holds the required information.

We could for example re-use the preview page ID configuration to assume a single site.
But to cover the case that records might be shown on multiple sites, we would need to introduce TSConfig setting
which lets developers add multiple sites in which these records will be rendered.

Additionally, if feasible, it would be nice to also disallow adding a storage page to plugin settings, which is not suitable for the site this plugin is on.