Improve Dockerfile

[Harvester57]

Hi !

This PR implements several best practices for the Dockerfile, mainly a multi-stage build process to significantly reduce the final image size (from 1.4GB to 209MB while building with containerd on a Windows host, a 85% reduction) and build time. The patched DHCP client is built in a transient builder stage, and then copied in a clean Debian 13 slim base.

It is building fine on my Windows system, but I have no way to currently test that it still runs correctly when launched, could you have a go at it and let me know if there is no regression ?

Highlights

• Multi-Stage Build Implementation: The Dockerfile has been refactored to use a multi-stage build pattern, separating the build environment (builder stage) from the final runtime environment. This significantly reduces the final image size by not including build-time dependencies.
• Optimized Base Images: The base image for the final stage has been switched to debian:13-slim, and both base images now use specific SHA256 digests for enhanced security and reproducibility. The builder stage uses debian:13.
• Consolidated RUN Commands and Cleanup: Multiple RUN commands have been chained together using && \ to reduce the number of Docker image layers. Aggressive cleanup steps, including apt-get clean and rm -rf /var/lib/apt/lists/*, are now integrated into the installation processes to minimize image bloat.
• Efficient Build Process: The build process for dhclient-orange-patched now uses make -j$(( $(nproc) + 1 )) for parallel compilation, and git clone uses --depth 1 for faster cloning. Build-time dependencies like build-essential and git are confined to the builder stage.
• Non-Interactive Package Installation: The ARG DEBIAN_FRONTEND=noninteractive instruction has been added to both build stages to prevent interactive prompts during package installations, ensuring a fully automated build.

[Raraph84]

It seems good to me but I won't have the time to test this before january, I will update here when I've tested it