Load KDE QtQuickSettings in Discover

Summary:
As per other QtQuick parts of Plasma

CCBUG: 400908

Test Plan: Compiles. Code is copy pasted from working projects.

Reviewers: Plasma, apol

Reviewed By: apol

Subscribers: apol, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D16811