Allow restoring an expired shared link

[kolAflash]

Currently a user may not notice when a link is going to expire.
Either because the user forgot, or because the admin set a global expiration default and the user didn't noticed that at all.
This is especially a problem, if a link has been laboriously spread over multiple channels (newsletters, Twitter, ...).
 

So the user should be better informed about the expiration of a link.
At first when the link is being created.
And maybe also later, before the link is expiring (e.g. sending an email one day before expiration).
 

Additionally it could be helpfull, if there's a possibility to restore an expired link.
At least for a certain time after it's been expired.

Maybe a link should be restoreable for the same time it was active. So if the link was active for six month, it should stay restoreable for another six month.

[dajusc]

Meanwhile in NC21 there is an email notification after a link is expired, which is only of limited help.
As @kolAflash proposed it would be very helpful to have:

1. A notification before the link expires
2. A possibility to restore an expired link

[Flo-MF]

There is a OCC command available, to send a notification about expiring shares, which you can run by a cronjob:

occ sharing:expiration-notification

https://docs.nextcloud.com/server/latest/admin_manual/configuration_files/file_sharing_configuration.html#get-a-notification-before-a-share-expires

[joshtrichards]

Adjusted the title to focus on the "restoring a shared link" part of the enhancement request, since sending a notification before a share expires is already a possibility today.