Add an option to confirm trash emptying into settings

Summary:
Add an option to confirm trash emptying into settings.

BUG: 340572

Reviewers: #dolphin, ngraham, markg

Reviewed By: #dolphin, ngraham, markg

Subscribers: markg, ngraham, rkflx, #dolphin

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D10968