fix: [letsencrypt] scheduled call to compose would fail

Because it was requiring ``COMPOSE_LAUNCHER_OPTS`` to be set in the
cron file.

letsencrypt/hooks/schedule_command-relation-joined

@@ -25,6 +25,8 @@ fi
 ## Warning: 'docker -v' will use HOST directory even if launched from
 ##   'cron' container.
 file_put "$DST" <<EOF
+COMPOSE_LAUNCHER_OPTS=$COMPOSE_LAUNCHER_OPTS
+
 $schedule     root  lock $label -D -p 10 -c "\
     compose crt $SERVICE_NAME renew" 2>&1 | ts '\%F \%T \%Z' >> $LOCAL_LOG