Enable HTTP/2 protocol support

[GabrielMajeri]

The HTTP/2 protocol is a powerful improvement over the initial version of the HTTP protocol, which should lead to much faster connection speeds for our users.

I've found this blog post describing how to enable HTTP/2 support in Apache 2 running inside a Docker container. I haven't tried out the steps yet, but this GitHub issue seems to suggest that it might not be possible (or it might be very hard) to get this feature working correctly on Apache. The comments there instead propose switching to NGINX with PHP-FPM for better H2 support. If this is the case, this is a starting point for an NGINX config file for hosting osTicket.