utils/resolver.go
func NewRegistryResolver(opt registry.Opt) Resolver {
	return &registryResolver{
		opt:   opt,
		cache: make(map[string]string),
	}
}
func NewRegistryResolver(opt registry.Opt) Resolver {
	return &registryResolver{
		opt:   opt,
		cache: make(map[string]string),
	}
}
// NewRegistryResolver returns a resolver that looks up a docker
// registry to resolve digests