feat(jigasi): support graceful shutdown via sidecar (#1908)

jigasi/rootfs/opt/jitsi/shutdown.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/with-contenv bash
+
+if [ -n "$AUTOSCALER_URL" ]; then
+    # notify the sidecar of imminent shutdown
+    PORT=${AUTOSCALER_SIDECAR_PORT:-6000}
+    curl -d '{}' -v 0:$PORT/hook/v1/shutdown
+    sleep 10
+fi
+
+# shutdown everything
+s6-svscanctl -t /var/run/s6/services