fix: restore foris config from snapshots

Hotfixes https://gitlab.nic.cz/turris/turris-os-packages/-/issues/657

updater/fix/files/config-foris-restore

+#!/bin/sh
+set -eu
+
+config="/etc/config/foris"
+
+if [ ! -s "$config" ]; then
+	schnapps list | awk 'NR > 2 { print $1 }' | sort -rn \
+		| while read -r snapshot; do
+			schnapps mount "$snapshot" >/dev/null
+			mntp="/mnt/snapshot-@$snapshot"
+			if [ -s "${mntp}${config}" ]; then
+				cp -a "${mntp}${config}" "$config"
+				umount "$mntp"
+				exit 0
+			fi
+			umount "$mntp"
+		done
+fi
+
+if [ ! -s "$config" ]; then
+	echo "Failed to locate latest non-empty version of /etc/config/foris in snapshots! Config is empty and wizard has to be performed again." >&2
+	exit 1
+fi