add -pid parameter to Snore backend calls

Summary: the upcoming change to SnoreToast also accepts process id. Since we can supply PID, why not? :)

Reviewers: KDE Connect, Frameworks, vonreth

Reviewed By: vonreth

Subscribers: kde-frameworks-devel, vonreth

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D23282