Support priv/unpriv image extraction

Optionally add back privileged extraction which can be enabled with
LUET_PRIVILEGED_EXTRACT=true

Signed-off-by: Ettore Di Giacinto <mudler@sabayon.org>

vendor/github.com/moby/buildkit/session/filesync/filesync.proto

@@ -0,0 +1,20 @@
+syntax = "proto3";
+
+package moby.filesync.v1;
+
+option go_package = "filesync";
+
+service FileSync{
+  rpc DiffCopy(stream BytesMessage) returns (stream BytesMessage);
+  rpc TarStream(stream BytesMessage) returns (stream BytesMessage);
+}
+
+service FileSend{
+  rpc DiffCopy(stream BytesMessage) returns (stream BytesMessage);
+}
+
+
+// BytesMessage contains a chunk of byte data
+message BytesMessage{
+	bytes data = 1;
+}