live: change the way flatpak setup works

instead of seeding the flatpaks manually let's just use the tree from
installation. we'll put that into /@flatpak and then mount it into place
as part of the live generator.

we'll see how it goes.

if this works out we may then btrfs receive the volume into the
installed system and handle it similar to @snap as a special subvol

mkosi.extra/usr/bin/_kde-linux-live-setup

@@ -52,5 +52,3 @@ cp /usr/share/applications/calamares.desktop /home/live/Desktop/
 chmod +x /home/live/Desktop/calamares.desktop # without this there'd be a dialog asking if it really should execute
 
 chown -R live:live /home/live/
-
-_kde-linux-install-flatpaks

mkosi.extra/usr/lib/systemd/system-generators/kde-linux-live-generator

@@ -39,3 +39,21 @@ EOF
 
 mkdir "$normal_dir/multi-user.target.wants/"
 ln -s ../system.mount "$normal_dir/multi-user.target.wants/system.mount"
+
+cat <<- EOF > "$normal_dir/var-lib-flatpak.mount"
+# Generated by $(basename "$0")
+[Unit]
+Description=Mount unit for /var/lib/flatpak
+
+[Mount]
+What=/dev/disk/by-label/KDEOSLive
+Where=/var/lib/flatpak
+Type=btrfs
+Options=rw,subvol=@flatpak
+
+[Install]
+WantedBy=multi-user.target
+EOF
+
+mkdir "$normal_dir/multi-user.target.wants/"
+ln -s ../var-lib-flatpak.mount "$normal_dir/multi-user.target.wants/var-lib-flatpak.mount"

mkosi.postinst.chroot

@@ -211,8 +211,7 @@ flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.f
 # Do this separately, when used as part of remote-add it complains about GPG for unknown reasons
 flatpak remote-modify --collection-id=org.flathub.Stable flathub
 flatpak install --noninteractive --assumeyes org.mozilla.firefox
-flatpak create-usb flatpak org.mozilla.firefox
-rm -rf /var/lib/flatpak # reset the state in the image
+mv /var/lib/flatpak / # we'll extract this and later mount it into place
 
 plymouth-set-default-theme breeze-bgrt