improve nginx config to avoid "listen ... http2 directive is deprecated" warning

[mrjones-plip]

Describe the issue
When starting nginx there's an error:

nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in /etc/nginx/nginx.conf:37
2023/09/23 00:03:13 [warn] 47#47: the "listen ... http2" directive is deprecated, use the "http2" directive instead in /etc/nginx/nginx.conf:38
nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in /etc/nginx/nginx.conf:38
2023/09/23 00:03:13 [notice] 47#47: signal process started

Per the note, we should use the non-deprecated config syntax to listen for http2 requests.

This is just a warning (not an error or fatal), but was introduced in #8451

Describe the improvement you'd like
Use correct syntax

Describe alternatives you've considered
ignore it! it won't break when we're least expecting it...right...RIGHT!?!?

[mrjones-plip]

here's the docs and the correct syntax is:

    server {
        listen    443 ssl;
        http2     on;
    }