Enable Apache to serve Horde via HTTPS

[ikselven]

At the moment, the Apache in the groupware-mail deployment serves Horde via HTTP only. This is fine for local development, where TLS is unnecessary. However for actual world-accessible scenarios, we want the Apache to serve Horde via HTTPS.

The groupware-mail deployment needs to be extended to support TLS.

Requirements are as follows:

• use of HTTP or HTTPS should be configurable, e.g. via .env
• if using HTTPS, Apache should automatically redirect from HTTP to HTTPS
• certificates will be provided by the user, but the deployment needs some means to make them available to Apache, e.g. via mount

The implementation of this feature also requires changes to Maintaina's Horde Apache image.

[ralflang]

The preferred strategy is to proxy and handle the SSL related stuff outside the container or enable mod_ssl and link a vhost dir into the container, including certificates.