scripts: add cron helper

scripts/cron.sh

+#!/bin/sh
+# usage:
+# 12 1 * * * /bin/sh /opt/rwm/scripts/cron.sh
+
+umask 077
+LOGFILE="/var/log/rwm/cron.log.$(date +'%Y-%m-%dT%H:%M:%S%z')"
+mkdir -p "$(dirname "$LOGFILE")"
+
+/opt/rwm/rwm.py --config /etc/rwm.yml backup-all 1>"$LOGFILE" 2>&1
+RET=$?
+
+if [ $RET = 0 ]; then
+	RESULT="OK"
+else
+	RESULT="ERROR"
+fi
+# shellcheck disable=SC2002
+cat "$LOGFILE" | mail -E -s "rwm backup-all $RESULT" $USER