Correctly scopes dolphin in systemd service `app-org.kde.dolphin.service` when dbus-activated (while still working if systemd is not present), as per https://systemd.io/DESKTOP_ENVIRONMENTS/
uses new ECM modules:
- https://invent.kde.org/frameworks/extra-cmake-modules/-/merge_requests/5 to simplify the systemd service templating + install
- https://invent.kde.org/frameworks/extra-cmake-modules/-/merge_requests/17 to generate the dbus service file automatically