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/prepare/50-ipv6.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+
+# This command reads the `DISABLE_IPV6` env var and will either enable
+# or disable ipv6 in all nginx configs based on this setting.
+
+log_info 'IPv6 ...'
+
+# Lowercase
+DISABLE_IPV6=$(echo "${DISABLE_IPV6:-}" | tr '[:upper:]' '[:lower:]')
+
+process_folder () {
+	FILES=$(find "$1" -type f -name "*.conf")
+	SED_REGEX=
+
+	if [ "$DISABLE_IPV6" == "true" ] || [ "$DISABLE_IPV6" == "on" ] || [ "$DISABLE_IPV6" == "1" ] || [ "$DISABLE_IPV6" == "yes" ]; then
+		# IPV6 is disabled
+		echo "Disabling IPV6 in hosts in: $1"
+		SED_REGEX='s/^([^#]*)listen \[::\]/\1#listen [::]/g'
+	else
+		# IPV6 is enabled
+		echo "Enabling IPV6 in hosts in: $1"
+		SED_REGEX='s/^(\s*)#listen \[::\]/\1listen [::]/g'
+	fi
+
+	for FILE in $FILES
+	do
+		echo "- ${FILE}"
+		sed -E -i "$SED_REGEX" "$FILE"
+	done
+
+	# ensure the files are still owned by the npmuser
+	chown -R npmuser:npmuser "$1"
+}
+
+process_folder /etc/nginx/conf.d
+process_folder /data/nginx