Even though `ActionView::Helpers::AssetTagHelper.preload_links_header`
is set to false, `preload_link_tag` sends the Link header if the total
header size to send is under 8K. However, this causes HTTP responses
to fail in NGINX if the default `proxy_buffer_size` is set too low.

Ironically because `app/views/layouts/_loading_hints.html.haml` is a
cached partial, `preload_link_tag` generates the HTML, but only
actually sends the `Link` header once a minute when the cache expires.
This suggests that the `Link` header isn't really helping much, and it
can cause more trouble than it's worth.

Rails 7.1 lowered the `preload_link_tag` limit to 1000 bytes in
https://github.com/rails/rails/pull/48405, but that may not be
sufficient.

https://github.com/rails/rails/issues/51436 proposes to disable the
sending of the Link header entirely. This patch does this by turning
send_preload_links_header into a NOP.

We can probably drop this patch for Rails 7.1 and up, but we might
want to wait for https://github.com/rails/rails/pull/51441 or some
mechanism that can disable the `Link` header.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/443866

Changelog: fixed