fix: schedule weekly full postgres backup

infra/install-postgres-backup-cron.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+set -eu
+
+temporary=$(mktemp)
+trap 'rm -f -- "$temporary"' EXIT HUP INT TERM
+
+crontab -l 2>/dev/null | grep -v 'postgres-backup.sh' > "$temporary" || true
+printf '%s\n' '30 3 * * 0 flock -n /tmp/miem-postgres-backup.lock /srv/miem_workers/infra/postgres-backup.sh >/dev/null 2>&1' >> "$temporary"
+crontab "$temporary"