jibri: adds autoscaler sidecar hook to signal final shutdown (#1810)

jibri/rootfs/opt/jitsi/shutdown.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/with-contenv bash
+# notify the sidecar of imminent shutdown
+PORT=${AUTOSCALER_SIDECAR_PORT:-6000}
+curl -d '{}' -v 0:$PORT/hook/v1/shutdown
+sleep 10
+
+# signal jibri to shutdown via rest api
+/opt/jitsi/jibri/shutdown.sh
+
+# shutdown everything else
+s6-svscanctl -t /var/run/s6/services