Move Message proto to types

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

api/types/event.proto

@@ -0,0 +1,33 @@
+/*
+	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.
+*/
+
+syntax = "proto3";
+
+package containerd.types;
+
+import "github.com/containerd/containerd/api/types/fieldpath.proto";
+import "google/protobuf/any.proto";
+import "google/protobuf/timestamp.proto";
+
+option go_package = "github.com/containerd/containerd/v2/api/types;types";
+
+message Envelope {
+  option (containerd.types.fieldpath) = true;
+  google.protobuf.Timestamp timestamp = 1;
+  string namespace = 2;
+  string topic = 3;
+  google.protobuf.Any event = 4;
+}