JSON is a much better supported format than HCL.

Change-Id: Ieb82b8a5ff71f57502d926b9418274cbd5a1fe2a

As we wish to support multi-platform builds, docker-compose.yaml has
been replaced in favor of docker-bake.json.

Change-Id: I170ca43bcaca6412773df8f3748f324d2e8da823

This update informs the user how to build using `docker buildx`.

Change-Id: I9f15379a9b309f51654aa542f59954639ff653e6

Change-Id: I4ffad85f291d00149f8f67192e453a9ee65e0240

This does not appear to be used and therefore should not be regularly
rebuilt. The images already stored in the registry will remain
available.

Change-Id: Ie9e4dda82d32f4403b9e64a34aba540a5b885be9

This does not appear to be used by the project and therefore should not
be regularly rebuilt and uploaded to our registry. Images already on the
registry shall remain.

Change-Id: I22c4ea5ced7428912eed2d2b5f0e1960702da5ea

Now 22.04 is compiled using buildx with multi-platform, we can reference
this image directly and remove the need for duplication of the
Dockerfile.

Change-Id: Id6a8459bc0eedaea2ed94002ee9cbd812ee72b1f

* Ups the action versions where possible.
* Improves the comments.
* Corrects indentation.
* bake-action Action references "docker-bake.json" instead of
  "docker-bake.hcl".
* artifact downloaded to "downloaded-dockerfiles" dir.

Change-Id: I21b304637856f2faa213b56be12634b339b7576c

It doesn't make much sense to have these build to ARM or RISC-V
platforms.