Update s6-overlay and move processes to new format

docker/rootfs/etc/s6-overlay/s6-rc.d/frontend/run

@@ -0,0 +1,15 @@
+#!/command/with-contenv bash
+# shellcheck shell=bash
+
+set -e
+
+# This service is DEVELOPMENT only.
+
+if [ "$DEVELOPMENT" == "true" ]; then
+	cd /app/frontend || exit 1
+	# If yarn install fails: add --verbose --network-concurrency 1
+	yarn install
+	yarn watch
+else
+	exit 0
+fi