docker: add gunicorn based docker image

[foosinn]

This pull request updates the Dockerfile to optimize the build process and reduce image size. Changes include:

• Using a multi-stage build with a smaller base image (python:3.12-slim) for the builder stage.
• Incorporating Gunicorn to serve the application, enhancing performance and scalability.
• Implementing COPY --from=builder to include only necessary files from the builder stage in the final image.