Adds support to run processes as a user/group, defined

with PUID and PGID environment variables

- Detects if image is run with a user in docker command and fails if so
- Adds s6 prepare scripts for adding a 'npmuser'
- Split up and refactor the s6 prepare scripts
- Runs nginx and backend node as 'npmuser'
- Changes ownership of files required at startup

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

@@ -3,17 +3,20 @@
 
 set -e
 
-echo "❯ Starting backend ..."
+. /bin/common.sh
+
+log_info 'Starting backend ...'
+
 if [ "$DEVELOPMENT" == "true" ]; then
 	cd /app || exit 1
 	# If yarn install fails: add --verbose --network-concurrency 1
-	yarn install
-	node --max_old_space_size=250 --abort_on_uncaught_exception node_modules/nodemon/bin/nodemon.js
+	s6-setuidgid npmuser yarn install
+	exec s6-setuidgid npmuser node --max_old_space_size=250 --abort_on_uncaught_exception node_modules/nodemon/bin/nodemon.js
 else
 	cd /app || exit 1
 	while :
 	do
-		node --abort_on_uncaught_exception --max_old_space_size=250 index.js
+		s6-setuidgid npmuser node --abort_on_uncaught_exception --max_old_space_size=250 index.js
 		sleep 1
 	done
 fi