Pulp - Refactor #765: Convert Pulp to use MongoEngine
Convert the DockerManifest model to use mongoengine model
As per https://pulp.plan.io/issues/967, a new DockerManifest model has been created. However, as it was created against the 2.6 branches, it has not been converted to the new-style model type yet. This task is to earmark the conversion work.
- A "new-style" model for the DockerManifest model, part of the Docker v2 API.
- Follow the conversion guide
The Docker data type is documented here: https://github.com/docker/distribution/blob/release/2.0/docs/spec/manifest-v2-1.md