To avoid compounded round trips leading to slow retrieval of manifests with a
large number of signatures, the fetch of signatures has been parallelized. This
simply spawns a goroutine for each path, coordinated with a sync.WaitGroup.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
Add a SignatureService and expose it via Signatures() on Repository so
external integrations wrapping the registry can access signatures.
Move signature related code from revisionstore.go to signaturestore.go.
Signed-off-by: Andy Goldstein <agoldste@redhat.com>