add istio_feature.proto for feature https://docs.google.com/document/…

common-protos/istio.io/extensions/istio_feature.proto

@@ -0,0 +1,48 @@
+// Copyright 2019 Istio 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 istio.extensions;
+
+option go_package="istio.io/api/istio.io/extensions";
+
+import "google/protobuf/descriptor.proto";
+
+// Values applied at the field level
+extend google.protobuf.FieldOptions {
+	// the reason why is 2022 is that this PR may be merged in this year ^_^ 
+	IstioFeature feature = 2022;
+}
+
+enum FeatureStatus {
+	UNSET = 0;
+	ALPHA = 1;
+	BETA = 2;
+	STABLE = 3;
+	EXPERIMENTAL = 4;
+}
+
+// These options should be used during schema definition, applying them to some of the fields in protobuf
+// Below are 1 related repo and 1 PR for this repo:
+// Repo: https://github.com/istio/enhancements
+// Repo PR: https://github.com/istio/enhancements/pull/88
+message IstioFeature {
+	// label the feature's status, available status values may be alpha, beta and stable 
+	// there would be experimental in future.
+	FeatureStatus status = 1;
+	// id means the feature id which can be mapped here: https://github.com/istio/enhancements/blob/master/features.yaml
+	// it should be contained in id section of features under this yaml file.
+	string id = 2;
+}