Move protobuf package under pkg

Signed-off-by: Derek McGowan <derek@mcg.dev>

pkg/protobuf/types/types.go

@@ -0,0 +1,28 @@
+/*
+   Copyright The containerd Authors.
+
+   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 types provides convinient aliases that make google.golang.org/protobuf migration easier.
+package types
+
+import (
+	"google.golang.org/protobuf/types/known/anypb"
+	"google.golang.org/protobuf/types/known/emptypb"
+	field_mask "google.golang.org/protobuf/types/known/fieldmaskpb"
+)
+
+type Empty = emptypb.Empty
+type Any = anypb.Any
+type FieldMask = field_mask.FieldMask