First boot setup wizard and tuigreet integration

This MR is the first end-to-end try of implementing the new System Image V5 onboarding:

• Unless setup is completed, agetty autologins "root" (which has no pw anyway)
• The shell starts reform-setup in a special sway environment via a script in /etc/profile.d
• This sway is configured by the file /etc/reform-setup-sway-config
• greetd is installed (via Debian) and tuigreet binary dropped in /usr/bin
• Reform Setup Wizard writes /etc/greetd/config.toml with sway or wayfire preselected (users can change this in tuigreet or in this file)
• After successfuly completion, Reform Setup Wizard runs its cleanup.sh which 1. removes root autologin 2. removes itself from /etc/profile.d 3. enables and starts greetd

mkimage.sh

@@ -247,10 +247,12 @@ set -- "$@" \
 	--customize-hook='printf "[Service]\nExecStart=\nExecStart=-/sbin/agetty --autologin root --noclear %%I \$TERM\n" > "$1"/etc/systemd/system/getty@tty1.service.d/override.conf' \
 	--customize-hook='copy-in reform-setup-sway-config /etc' \
 	--customize-hook='copy-in reform-setup /usr/bin' \
+	--customize-hook='copy-in reform-setup-cleanup.sh /usr/libexec' \
 	--customize-hook='copy-in tuigreet /usr/bin' \
 	--customize-hook='chmod 755 "$1"/usr/bin/reform-setup' \
+	--customize-hook='chmod 755 "$1"/usr/libexec/reform-setup-cleanup.sh' \
 	--customize-hook='chmod 755 "$1"/usr/bin/tuigreet' \
-	--customize-hook='echo "/usr/bin/sway --config /etc/reform-setup-sway-config" > "$1"/etc/profile.d/reform-setup'
+	--customize-hook='echo "/usr/bin/sway --config /etc/reform-setup-sway-config" > "$1"/etc/profile.d/reform-setup.sh'
 # populate /etc
 set -- "$@" \
 	--essential-hook='{ echo LABEL=reformsdroot / auto errors=remount-ro 0 1; echo LABEL=reformsdboot /boot auto errors=remount-ro 0 1; } > "$1"/etc/fstab' \