Introduced in https://github.com/gem5/gem5/pull/236 the
"docker-build.yaml" file will allow us to build and push docker images
to the GitHub Container Registry. This allows for both automation of
docker image building and allows us to utilize Github's zero-cost
pulling policy for downloads to GitHub Actions runners.
In this PR https://github.com/gem5/gem5/pull/236 has been altered to
use Docker `buildx` which allows for multi-platform Docker Image builds.
A multi-platform Docker image pull automatically pull the correct image
for your platform from a single URL. In this prototype the images are
build to both `linux/arm64` and `linux/amd64` have been set.
Docker `buildx` has it's own file format for specifying image builds
called `bake`. "util/dockerfiles/docker-bake.hcl" has been added with
the goal of replacing "util/dockerfiles/docker-compose.yaml".
In this proof-of-concept doesn't build all our docker images, just
enough to ensure it works inside our actions as intended.
Change-Id: Id0debed216c91ec514aa4fce3bc2ff4fc2ea669b
