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/20-paths.sh

@@ -0,0 +1,41 @@
+#!/command/with-contenv bash
+# shellcheck shell=bash
+
+set -e
+
+log_info 'Checking paths ...'
+
+# Ensure /data is mounted
+if [ ! -d '/data' ]; then
+	log_fatal '/data is not mounted! Check your docker configuration.'
+fi
+# Ensure /etc/letsencrypt is mounted
+if [ ! -d '/etc/letsencrypt' ]; then
+	log_fatal '/etc/letsencrypt is not mounted! Check your docker configuration.'
+fi
+
+# Create required folders
+mkdir -p \
+	/data/nginx \
+	/data/custom_ssl \
+	/data/logs \
+	/data/access \
+	/data/nginx/default_host \
+	/data/nginx/default_www \
+	/data/nginx/proxy_host \
+	/data/nginx/redirection_host \
+	/data/nginx/stream \
+	/data/nginx/dead_host \
+	/data/nginx/temp \
+	/data/letsencrypt-acme-challenge \
+	/run/nginx \
+	/tmp/nginx/body \
+	/var/log/nginx \
+	/var/lib/nginx/cache/public \
+	/var/lib/nginx/cache/private \
+	/var/cache/nginx/proxy_temp
+
+touch /var/log/nginx/error.log || true
+chmod 777 /var/log/nginx/error.log || true
+chmod -R 777 /var/cache/nginx || true
+chmod 644 /etc/logrotate.d/nginx-proxy-manager