Update keycloak to version 8.0.0

[andifalk]

As part of updating to Keycloak 8.0 we should also follow another approach to automatically configure it with pre-defined clients, roles and users.

Attendees of the training should have the possibility to either

• use the download of the standard distribution of Keycloak 8.0 (https://www.keycloak.org/downloads.html) or
• use the Keycloak docker container (https://hub.docker.com/r/jboss/keycloak) if the attendee has docker installed

Then we have to provide the possibility to import a preconfigured realm with all required configurations for the practice labs (check if all configurations can be exported from the realm).