Docker: Reduce size of image using `FROM .. AS ..`

See https://docs.docker.com/engine/reference/builder/

Start with the Docker image build configuration and the Docker builder reference linked in the issue, focusing on multi-stage builds using `FROM ... AS ...`. Identify which build stages contribute to the final image and measure the result after separating them. Done means the generated image is smaller without breaking the package build.

索引モデルが issue の本文から書いたものです。