Summary:
All other KCMs have their {nav Get New [things]...} buttons in the bottom-right corner. This patch adjusts KWin's KCMs to adopt the same convention there too.

With this patch, all KCMs will have their GHNS buttons in the same location.

Closes T9954

Test Plan:
{F6375278}

{F6375277}

{F6375276}

{F6375275}

Reviewers: #kwin, #vdg, zzag

Reviewed By: #kwin, zzag

Subscribers: Codezela, kwin, kde-doc-english

Tags: #kwin, #documentation

Maniphest Tasks: T9954

Differential Revision: https://phabricator.kde.org/D16537