Generate docker image as part of CI pipeline
This removes the dependency on an externally generated docker image, and should make it easier to update the docker image or make other changes related to it. v2: * If the image doesn't exist, try pulling it from the main repo's registry. * Use debian:testing-slim as the base, might result in a slightly smaller image. v3: * Prevent installation of packages which are only recommended, for an even smaller image. * Add recommendation to remove new image from source repository in favour of the main repository's. Acked-by: Alex Deucher <alexander.deucher@amd.com> # v2