- [Improvement] When building images with
  `tutor images build --cache-to-registry`, use an OCI-compliant cache
  artifact format that should be universally compatible with all
  registries. This enables the use of that option when working with
  third-party registries such as [Harbor](https://goharbor.io/) or
  [ECR](https://aws.amazon.com/ecr/). Requires
  [BuildKit 0.12](https://github.com/moby/buildkit/releases/tag/v0.12.0)
  or later. (by @angonz and @fghaas)