[Feature]: support Caddy as a reverse proxy

[dkarlovi]

Feature description

Currently Nginx setup is supported, which is OK since Nginx is very robust tech.

In the meantime, there was a raise of new generation HTTP servers written in Go, such as Traefik and Caddy. My suggestion is to provide provisional Caddy config which would allow to successfully run Pimcore behind Caddy.

One reason for this is Mercure ships as a Caddy module now, and there's a RFC in Pimcore describing real-time two way communication with a Pimcore app via Mercure as a transport, so having this be streamlined makes sense.

[github-actions]

Thanks a lot for reporting the issue. We did not consider the issue as "Pimcore:Priority", "Pimcore:ToDo" or "Pimcore:Backlog", so we're not going to work on that anytime soon. Please create a pull request to fix the issue if this is a bug report. We'll then review it as quickly as possible. If you're interested in contributing a feature, please contact us first here before creating a pull request. We'll then decide whether we'd accept it or not. Thanks for your understanding.