Add nginx HTTP/3 support

[lukasbableck]

Description

This PR adds support for HTTP/3 with nginx.
It's not too different from HTTP/2, just a few more parameters and options in the vhost configs.
Support for HTTP/3 is only available in nginx 1.25+, which is currently only included in Ubuntu 24.10 (apparently this will be released just today :D), or of course can be installed via the packages provided by nginx directly.

There is only one small problem, which is why this PR is marked as a draft.
Just like with HTTP/2, the Host header is not required and some clients do not include this header in their request.

This could be fixed by adding the following line to the /etc/nginx/fastcgi_params file:
fastcgi_param HTTP_HOST $host;
This works pretty well for me, but could maybe cause issues for others(?)

$host uses the host name from the request line, or host name from the “Host” request header field, or the server name matching a request in this order.

Or, probably the preferred option, nginx "fakes" the Host header for HTTP/3 just like it does for HTTP/2 requests. See: https://mailman.nginx.org/pipermail/nginx-devel/2024-January/LCIUMLKCM2EBMEMTU3KXMW74AP2C4FYZ.html
However, this has not yet been implemented and I have also not found anything on whether this is actually planned or not.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Install nginx 1.25.0+, enable HTTP/3 in system settings, enable HTTP/3 per domain => clients should be able to use HTTP/3.

Test Configuration:

• Distribution: Debian 12
• Webserver: nginx 1.26.2 and 1.27.2 (current stable and mainline versions provided by nginx)
• PHP: 8.3 FPM

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[d00p]

Nice work, just a minor adjustment, but very helpful, thank you

[lukasbableck]

Since there has not been any changes to this in nginx yet I have been looking for another solution for the Host header problem.
Nginx recommends switching to the $host variable (there is actually a PR to change this in the default config nginx/nginx#236), but to keep the same behavior as before for HTTP/1 and HTTP/2 something like the following could be used maybe. It will only use $http_host if it is not empty, otherwise $host will be passed to PHP.
LMK what you think @d00p

fastcgi_param  HTTP_HOST 	  $host;
fastcgi_param  HTTP_HOST	  $http_host if_not_empty;