String freeze break request for Nautilus

Hello,

This kind of bad to not have dealt with earlier, but I’d like modify a
string in the settings schema and add a string to the preferences
window. Both pertain to size limits for thumbnailable files.

Here’s the MR with the changes visible: https://gitlab.gnome.org/GNOME/nautilus/merge_requests/126/diffs

Also attaching a screenshot from the preferences window with the new
string.

Best,
Ernestas Kulik