GenerateManifestObj returns a new manifest object along with its byte serialization, and a sub manifest object array, and a digest array of sub manifests for list-type manifests.

NewImageDestination generates an ImageDestination by repository, the repository string must include tag or digest.

NewImageSource generates a PullTask by repository, the repository string must include tag or digest, or it can only be used to list tags.

NoCache used to disable a blobinfocache.

ImageDestination is a reference of a remote image we will push to.

ImageSource is a reference to a remote image need to be pulled.