feat(files_sharing): allow not deleting expiring shares

[skjnldsv]

Fix #17996

Feature

Shares that expires are just deleted. Which leads to confusion.

• We don't even know if the share existed or not....
• With the new file request, we might want to extend the drop period time...
• We need more transparency

Solution

• Allow admins to disable share deletion on expiration (opt-in)
  
• Adds a new view to list all expired shares
  

Status

• Add admin setting
• Add api controller
• Add new view
• Add integration tests