GitLab

- based on openjdk:11-jre-slim instead of a base system and
    installing java manually
- removed git installation, we use a maven library for this
    no system installed git needed for anything
- removed this damn proxy env vars
    they have nothing to do baked into an docker image!!
- removed junit downloads
    not needed in backend. The testrunners are responsible
    for what they need
- removed setting of a specific profile
    in prod always the default one should be active,
    use a different profile on your dev machine which you
    DO NOT commit