WIP: Enable TLS v1.3 in NGINX

Now that we're shipping OpenSSL v1.1.1 and TLS v1.3 is becoming used more frequently, let's enable it by default. More details:

• https://wiki.openssl.org/index.php/TLS1.3
• https://blog.cloudflare.com/introducing-tls-1-3/

This mirrors the change made in Omnibus: gitlab-org/omnibus-gitlab!3458 (diffs)