feat: attempt at abstracting buildx config in bake file
A lot of configuration lives in .gitlab-ci.yml instead of the build definition. This PR introduces a bake file that contains the configuration. More at https://docs.docker.com/build/bake/reference.
With the bake file, we should be able to have more consistency between the CI pipelines on eicweb and GitHub.
Edited by Wouter Deconinck