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/util/apicaps/pb/caps.proto

@@ -0,0 +1,19 @@
+syntax = "proto3";
+
+package moby.buildkit.v1.apicaps;
+
+import "github.com/gogo/protobuf/gogoproto/gogo.proto";
+
+option (gogoproto.sizer_all) = true;
+option (gogoproto.marshaler_all) = true;
+option (gogoproto.unmarshaler_all) = true;
+
+// APICap defines a capability supported by the service
+message APICap {
+	string ID = 1;
+	bool Enabled = 2;
+	bool Deprecated = 3; // Unused. May be used for warnings in the future
+	string DisabledReason = 4; // Reason key for detection code
+	string DisabledReasonMsg = 5; // Message to the user
+	string DisabledAlternative = 6; // Identifier that updated client could catch.
+}