Compute the digest ourselves, the registry is in general untrusted and
computing it ourserlves is easy enough.
The stop passing the unverifiedCanonicalDigest value around, simplifying
ImageSource.GetManifest and related code. In particular, remove
retrieveRawManifest and have internal users just call Manifest() now that
we don't need the digest.
Does not change behavior. This is a straightforward move and update of
package references, except for:
- Adding a duplicate definition of manifestSchema1 to
cmd/skopeo/copy.go. This will need to be cleaned up later, for now
preferring to make no design changes in this commit.
- Renaming parseDockerImage to NewDockerImage, to both make it public
and consistent with common golang conventions.
