Add script to mark daily backup

scripts/mark_daily_backup.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+if [ "$EUID" -ne 0 ]; then
+  echo "This script must be run by the root user" >&2
+  exit 1
+fi
+
+if docker compose run --rm init sh -c '[ ! -L /backups/latest ]'; then
+   # There is no latest backup, nothing to do
+   exit 0
+fi
+
+if docker compose run --rm init sh -c '[ -e /backups/daily ]'; then
+    # Daily marker exists, update it
+    docker compose run --rm init sh -c '
+        rm /backups/daily &&
+        cp -P /backups/latest /backups/daily
+    ' || exit 1
+else
+    # Daily marker does not exist, create it
+    docker compose run --rm init cp -P /backups/latest /backups/daily || exit 1
+fi
+