Add entity plugin v proto file (#261)

Signed-off-by: Ian Chen <[email protected]>

proto/ignition/msgs/entity_plugin_v.proto

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2022 Open Source Robotics Foundation
+ *
+ * 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 ignition.msgs;
+option java_package = "com.ignition.msgs";
+option java_outer_classname = "EntityPluginVProtos";
+
+/// \ingroup ignition.msgs
+/// \interface EntityPlugin_V
+/// \brief An array of plugins for a entity.
+
+import "ignition/msgs/entity.proto";
+import "ignition/msgs/header.proto";
+import "ignition/msgs/plugin.proto";
+
+message EntityPlugin_V
+{
+  /// \brief Optional header data
+  Header header = 1;
+
+  /// \brief Entity the plugins belong to
+  Entity entity = 2;
+
+  /// \brief Plugin messages.
+  repeated Plugin plugins = 3;
+}