Expose KConfig settings to allow registration in KCM Notification

Summary: For KCM Notification, allow to register the generated settings to the ManagedConfigModule machinery

Test Plan: refactor, no change

Reviewers: #plasma, #frameworks, ervin, bport, davidedmundson, mart, meven

Subscribers: broulik, meven, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26047