shell-manager: Report a version

GNOME Settings fetches the version via DBus so report a version number but make it very obvious it's not the GNOME version to not raise false expectations.

Thanks to Jeremy Bicha for bringing this up.

What we could do is still parse gnome-desktop's XML and then say "based on 43.x" but that would trigger the same problems as the current XML parsing GNOME wants to avoid. What would be good is to have GNOME 43.0 (using phosh 0.20.0) to avoid possible confusion.

Signed-off-by: Guido Günther guido.gunther@puri.sm