Set base nginx worker_processes to auto

A single worker underutilizes multi-core CPUs. Using auto lets nginx
spawn one worker per CPU core for better concurrency.

template/base-nginx-conf.ejs

@@ -1,5 +1,5 @@
 user  nginx;
-worker_processes  1;
+worker_processes  auto;
 
 error_log  /var/log/nginx/error.log warn;
 pid        /var/run/nginx.pid;