Clean up Dockerfiles and docker-compose file

[fabianhauser]

The Docker and docker-compose files are currently a bit chaotic, and split into base, dev, production etc.
This makes the development setup hard to understand (and with that also to use). Also, if the upstream base container changes (e.g. for security reasons), this is currently only reflected after a manual rebuild of the base image.

Steps to clean that up:

• Get rid of docker-studentenportal-base
• Use multi-stage builds to get rid of build dependencies for the final image
• Move docker-compose-production.yml to deploy
  Reason: this compose file is not really a part of the studentenportal application, just how we choose to deploy it
  • We can probably stop cloning this repo in the deployment process with that
  • Add a docs file about deployment (i.e. look at the deploy repository and the compose file 😉)
• Create an easier to use / understand development environment
  • Create a VSCode Dev Container
  • Dependencies inside dev container or with venv?
  • Use Docker-Compose integration for postgres
  • Update development documentation accordingly
    • Add link to pycharm readme for the same thing