[kde-cli-tools] Add search ellipsis to label, make label more consistent with HIG

Summary: This patch renames the label "Find file type or filename pattern" to "Search for file type or filename pattern..."

Reviewers: #vdg, #plasma, plasma-devel, ngraham

Reviewed By: #vdg, ngraham

Subscribers: ngraham, apol, plasma-devel

Tags: #plasma

Maniphest Tasks: T10258

Differential Revision: https://phabricator.kde.org/D18044