run tasks as separate cgroup via systemd

this allows us to adjust the nice value and memory settings per task

part of #691

src/scripts/stoptask.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+set -eu -o pipefail
+
+if [[ ${EUID} -ne 0 ]]; then
+    echo "This script should be run as root." > /dev/stderr
+    exit 1
+fi
+
+if [[ $# -eq 0 ]]; then
+    echo "No arguments supplied"
+    exit 1
+fi
+
+if [[ "$1" == "--check" ]]; then
+    echo "OK"
+    exit 0
+fi
+
+task_id="$1"
+
+service_name="cloudron-task-${task_id}"
+
+systemctl kill --signal=SIGTERM "${service_name}"
+