Missing capabilities to modify Docker installation for SSL support

### Steps to reproduce

Try to use the docker installation on a linux server and add SSL Encryption to the web interface and see how much time you spend finding a minimal invasive method without modifying the docker containers itself.

### Expected behavior

There should be an easy and documented way to modify the docker images by e.g. environment variables to allow switching
from HTTP to HTTPS.
HTTPS is necessary. In these days it is unprofessional and a serious lack of risk awareness to spin up services using HTTP by default.
Just to be clear, no HTTPS (even with self signed certs) means everyone in the network can read the traffic easily in clear text.
Systems like ralph hold critical and often person related data. Therefor this is a necessary feature.

### Actual behavior

There is no easy way to modify without breaking the ability to update the images with a simple docker-compose

### Environment

Ubuntu 20.04, Ubuntu 18.04

* Ralph version: IDK the actual one
* Operating system: Ubuntu 20.04/18.04
* Method of installation: Deb package? Manual installation? Docker?
Docker