web: use env variables to set worker processes and connections

Use 2 new environment variables to allow setting the number of nginx worker processes and connections. Add the variables to the docker-compose file and to the nginx-conf where default values are also set.

web/rootfs/defaults/nginx.conf

@@ -1,10 +1,10 @@
 user www-data;
-worker_processes 4;
+worker_processes {{ .Env.NGINX_WORKER_PROCESSES | default "4" }};
 pid /run/nginx.pid;
 include /etc/nginx/modules-enabled/*.conf;
 
 events {
-	worker_connections 768;
+	worker_connections {{ .Env.NGINX_WORKER_CONNECTIONS | default "768" }};
 	# multi_accept on;
 }