Add real_ip setting to nginx example.

What does this MR do?

Changes the bundled NGINX configuration files to support real IP address.
reference:
https://docs.gitlab.com/omnibus/settings/nginx.html#configuring-gitlab-trusted_proxies-and-the-nginx-real_ip-module

Are there points in the code the reviewer needs to double check?

Nothing.

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

none.