[kio] Add ellipsis to search label in Cookies section

Summary: This patch adds the ellipsis to the search label of the Cookies section of Network --> Settings.

Reviewers: VDG, Plasma, kde-frameworks-devel, ngraham

Reviewed By: VDG, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks

Maniphest Tasks: T10258

Differential Revision: https://phabricator.kde.org/D18045