session: Add custom dconf profile

This causes the cosmic-session to have a separate
writable dconf-database (while still inheriting
the default user database).

This will (partially) prevent issues such as
https://github.com/pop-os/cosmic-epoch/issues/1174
in the future, as other desktops won't pick up
cosmic's dconf profile.

data/dconf/profile/cosmic

@@ -0,0 +1,2 @@
+user-db:cosmic
+user-db:user

data/start-cosmic

@@ -37,6 +37,7 @@ export MOZ_ENABLE_WAYLAND=1
 export QT_QPA_PLATFORM="wayland;xcb"
 export QT_AUTO_SCREEN_SCALE_FACTOR=1
 export QT_ENABLE_HIGHDPI_SCALING=1
+export DCONF_PROFILE=cosmic
 
 if command -v systemctl >/dev/null; then
     # set environment variables for new units started by user service manager

debian/cosmic-session.install

@@ -0,0 +1 @@
+data/dconf/profile/cosmic /usr/share/dconf/profile/