Adoption of KUserFeedback for Discover

Summary:
Creates components so it can be integrated in any Kirigami application though.
Haven't tested custom information providers yet, need to get hold of a server
first to see how it will play out.

Depends on D24010
Depends on D24011

Reviewers: #plasma, vkrause, ngraham

Reviewed By: ngraham

Subscribers: ngraham, mart, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D5961