Make it possible to enforce a maximum expiry date for public links

[oparoz]

Steps to reproduce

1. As an admin, enforce an expiry date
2. As a user, share a file via public link

Expected behaviour

I should be able to select a custom expiry date which is not beyond what was set by the admin

Actual behaviour

I cannot set my own expiry date

[enoch85]

Related #4525

[ArtificialOwl]

It seems to be working like defined as Expected behaviour on NC12

[oparoz]

Fixed in 12. Thanks for the heads up.