Add Docker BuildX config (backport #266)

[mergify]

Changes Made

Adds a .docker/docker-bake.hcl buildx bake configuration file. The default behavior is to pulls images from ghcr.io/robotic-decision-making-lab/blue to prime the cache, but only push to local cache.

Also updates the Github action to use buildx-bake. In CI it overrides the default config to cache to/from images in the Github package registry.

All docker images ('ci', 'robot', 'desktop' and 'desktop-nvidia') can be built with:

cd .docker && docker buildx bake

This is a standalone PR with the buildx config; very similar files are commited in the more complex #241. If merged, this will lead to a conflict in that PR which will need to be managed by hand.

Associated Issues

Related to #241

Testing

Above docker buildx bake call completes successfully. Resulting images for rolling are functional to complete joystick teleop demo.

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This is an automatic backport of pull request #266 done by Mergify.

[mergify]

Cherry-pick of a8681d0 has failed:

On branch mergify/bp/humble/pr-266
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit a8681d0.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   .docker/docker-bake.hcl
	modified:   .gitignore

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .github/workflows/docker.yaml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally