Document how to use HTTP/2 nginx with GDK

Overview

We currently don't have any documentation / logic currently that allows HTTP2 to be used with nginx easily.

Proposal

We have https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/master/doc/howto/https.md which talks about how to enabled HTTPS but it would be helpful I feel to create a basic nginx/HTTP version which is then extended to document HTTPS and then also HTTP2.