Refine release process docker

[gerardo-navarro]

Why? This gives us the possibilit to build a production release anytime we want regardless if the code is released or not.

This issue includes:

• Dockerfile combining development and production using https://docs.docker.com/develop/develop-images/multistage-build
• Refine Dockerfile
• Adjust docker-compose.yml to build only target development, see https://docs.docker.com/develop/develop-images/multistage-build/#stop-at-a-specific-build-stage
• Github Action to build docker image and publish docker image
• Discuss the release flow; when should the docker release be triggered
• Connect docker image to repository
• Adjust README
• Abandon mindwendel-docker project