libnotificationmanager : add app-specific kconfig settings

Summary: Provide a kcfg for app-specific notifications with kconfig. Require D27059 and D27133

Reviewers: ervin, broulik, bport, meven

Reviewed By: ervin, bport, meven

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D27155