Set default differ for the default unpack config of transfer service

Signed-off-by: Henry Wang <henwang@amazon.com>
(cherry picked from commit a083b669c9412eef55ee103fe2bb1dec7c6178bc)

defaults/defaults_snapshotter_linux.go

@@ -21,4 +21,6 @@ const (
 	// This will be based on the client compilation target, so take that into
 	// account when choosing this value.
 	DefaultSnapshotter = "overlayfs"
+	// DefaultDiffer will set the default differ for the platform.
+	DefaultDiffer = "walking"
 )

defaults/defaults_snapshotter_unix.go

@@ -23,4 +23,6 @@ const (
 	// This will be based on the client compilation target, so take that into
 	// account when choosing this value.
 	DefaultSnapshotter = "native"
+	// DefaultDiffer will set the default differ for the platform.
+	DefaultDiffer = "walking"
 )

plugins/transfer/plugin_defaults_other.go

@@ -28,6 +28,7 @@ func defaultUnpackConfig() []unpackConfiguration {
 		{
 			Platform:    platforms.Format(platforms.DefaultSpec()),
 			Snapshotter: defaults.DefaultSnapshotter,
+			Differ:      defaults.DefaultDiffer,
 		},
 	}
 }