new: [myc-update] add configurable post scripts

bin/myc-update

@@ -128,4 +128,15 @@ for keyfile in {/root,/home/debian}/.ssh/authorized_keys; do
     sed -ri 's%^ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDri3GHzDt0Il0jv6zLjwkge48dN9tv11sqVNnKoDeUxzk4kn7Ng5ldd3p6dYL6Pa5NDqJUAhO/d/q08IWuwfEbtj8Yc/EkahcRwVD2imPceUeDgyCaOJhq7WO4c9d9yG8PnRO2\+Zk92a9L5vuELVLr4UHIQOs2/eFRY2/ODV8ebf5L1issGzfLd/IPhX5oJwMwKfqIFOP7KPQ26duHNRq4bYOD9ePW4shfxmyQDk6dSImFat05ErT\+X7703PcPx/PX2AIqqz95zqM6M26BywAohuaD5joxKgkd/mMIJylvT8GEYDlcLMHwnM7LtwtyJ1O9dkVpsibIqGy20KlAOGPf admin@0k$%ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMV3USt/BLnXnUk7rk8v42mISZaXBZuULbh2vx2Amk7k admin@old0kreplacement%g' "$keyfile"
 done
 
+
+for script in /etc/myc-update/post.d/*.sh; do
+    [ -e "$script" ] || continue
+    [ -x "$script" ] || {
+       echo "Skipping no-executable $script"
+       continue
+    }
+    "$script"
+done
+
+
 printf "Update finished ${GREEN}successfully${NORMAL} ${GRAY}(in %.2fs)${NORMAL}.\n" "$((SECONDS - start))"