Add configuration options to local transfer service

Signed-off-by: Tony Fang <nhfang@amazon.com>

pkg/transfer/transfer.go

@@ -20,10 +20,10 @@ import (
 	"context"
 	"io"
 
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/images"
-	"github.com/containerd/containerd/pkg/unpack"
-	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
 type Transferrer interface {
@@ -86,8 +86,15 @@ type ImageExportStreamer interface {
 }
 
 type ImageUnpacker interface {
-	// TODO: consider using unpack options
-	UnpackPlatforms() []unpack.Platform
+	UnpackPlatforms() []UnpackConfiguration
+}
+
+// UnpackConfiguration specifies the platform and snapshotter to use for resolving
+// the unpack Platform, if snapshotter is not specified the platform default will
+// be used.
+type UnpackConfiguration struct {
+	Platform    ocispec.Platform
+	Snapshotter string
 }
 
 type ProgressFunc func(Progress)