Switch nginx worker process to auto

[matburt]

This uses some internal logic from nginx to determine the optimal
number of worker processes given the available number of cores (and
some other details).

This might help busier systems.

[shanemcd]

Concern I raised to @matburt:

I’m wondering what would happen if you’re running in a container on a Kubernetes node that has 16 cores. But you limit the pod to only 10% of the CPU cycles. Is it going to create 16 worker processes and then they’re constantly fighting each other?

[wenottingham]

@shanemcd probably depends on what your container runtime mounts as its /proc or /sys vis-a-vis cgroups/namespaces

[shanemcd]

Regarding the concern I raised: nginxinc/docker-nginx#31

Edit: The official nginx images hardcode 1: https://github.com/nginxinc/docker-nginx/blob/master/stable/alpine/nginx.conf#L3