Move pkg/* to internal/*

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/modify/modify.go

@@ -0,0 +1,28 @@
+/*
+# Copyright (c) 2021, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+*/
+
+package modify
+
+import (
+	"github.com/NVIDIA/nvidia-container-toolkit/pkg/oci"
+)
+
+//go:generate moq -stub -out modify_mock.go . Modifier
+
+// Modifier defines an interface for modifying an OCI Specification.
+type Modifier interface {
+	Modify(oci.Spec) error
+}