Enable docker-compose for GPUs & Add public UI image

[tholor]

Proposed changes:

• docker-compose finally allows a way to directly enable GPU resources: https://docs.docker.com/compose/gpu-support/
  Prerequisite: You still need to have the nvidia-container-runtime installed on your host https://docs.docker.com/config/containers/resource_constraints/#gpu

So you can now run the "demo-stack" via:

docker-compose -f docker-compose-gpu.yml up -d

• Adding the public UI image to ensure that we have compatible versions and do not always need to build locally
• Removing pull_policy as this caused trouble with earlier docker-compose versions and even with most recent version did not work on all machines as intended