Add headers-more-nginx-module to base nginx

[sylvesterdamgaard]

Motivation

Standard nginx only exposes add_header, which can only add headers. There's no way to strip or rewrite headers nginx (or upstream) emits. This shows up in two common scenarios for users of the image:

• Replacing the default Server header. Security audits routinely flag the version-leaking nginx/1.x.x server header. server_tokens off reduces it to plain nginx, but lots of teams want a custom brand string ("Acme API", "Foo Marketing") or no Server header at all.
• Removing redundant or noisy headers added by upstreams or PHP-FPM (e.g. X-Powered-By, X-Generator).

add_header cannot do either. The community standard is the headers-more-nginx-module, which provides more_set_headers and more_clear_headers.

Proposal

• Compile headers-more-nginx-module into the nginx build for all php-fpm-nginx variants
• Optionally surface a small ENV convenience: NGINX_SERVER_HEADER → emits more_set_headers 'Server: $value' when set

Cost

• ~50 KB to image size
• No runtime overhead (statically compiled into nginx binary)
• Widely deployed, stable upstream module

Acceptance criteria

• more_set_headers directive available in all php-fpm-nginx images
• more_clear_headers directive available
• Documented in configuration reference
• Optional NGINX_SERVER_HEADER ENV var (or equivalent) for the common server-rebrand case