improve local setup for django application

this small addition adds a ports block to the django container in the docker-compose.test.yml setup such that the web app can be opened from the client (useful for showcasing and experimenting with stuff). Once the container has been build and started with

docker compose -f docker-compose.test.yml build
docker compose -f docker-compose.test.yml up

one can navigate to the project in the browser at http://0.0.0.0:8002/admin/ and the thredds-server can be accessed at http://0.0.0.0:8001/thredds/

ping @bjoern.sass

note that one needs to create a superuser when playing around with this. e.g. via

docker compose -f docker-compose.test.yml exec django python manage.py createsuperuser