* The previous export path pointing to '/tmp' in the container was causing problems when migrating to new versions due to permissions.
* Additionally remove obsolete version tag in docker-compose.yml.

* Since keycloak communicates with the auth-proxy,  trust issues can arise (TUW certs are signed by GEANT)
* To do that, we now switch to a custom image build for keycloak
* The custom image name includes the version number of the actual keycloak version to be pulled (it is an env variable and passed as an argument to the Dockerfile for pull)