Adds a nix flake with the following features/enhancements:
- builds docker image without qemu/root
nix developenvironment with compatibility to
- ci infrastructure for docker build and caching
- adds a nix binary cache hosted with cachix
- currently in the cachix account of @fpletz
The new nix-deps job that runs before all other jobs takes less than one minute if nothing needs to be built in case everything is already cached.