add system integration to NSIS installer of KDE Connect
Summary: https://i.imgur.com/4OYaaWW.jpg
Test Plan: install this to test : https://drive.google.com/file/d/1WAYnVDrgXvWR6EQ50tOgfFdQKv_fTC7s/view?usp=sharing
Reviewers: vonreth, albertvaka, sredman
Reviewed By: vonreth
Tags: KDE Connect
Differential Revision: https://phabricator.kde.org/D23577