Properly expose Minio server

[holtgrewe]

Is your feature request related to a problem? Please describe.
The Minio server is not properly exposed currently.

Describe the solution you'd like
Add configuration that exposes the server through port 9000 on the host via traefik. Effectively, the default configuration is then:

• <catch-all hostnames>:80 -- HTTP, redirect to HTTPS
• <catch-all hostnames>:443 -- HTTPS, server varfish-server
• <catch-all hostnames>:9000 -- HTTPS, server minio

Users may want to configure different hostname and expose minio via HTTPS on their hostname. This will require more special configuration, in particular when custom certificates are used. We should provide some example configuration as a docker-compose.override.yml fragment.

• default configuration
• override YAML fragment for different hostnames

Describe alternatives you've considered
N/A

Additional context
N/A