Add initial backend.proto

Signed-off-by: Michael Crosby <[email protected]>

backend/v1/backend.proto

@@ -0,0 +1,17 @@
+syntax = "proto3";
+
+package com.docker.api.backend.v1;
+
+import weak "gogoproto/gogo.proto";
+import "google/protobuf/empty.proto";
+
+option go_package = "github.com/docker/api/backend/v1;v1";
+
+service Backend {
+	// BackendInformation returns implementation specific information on the backend.
+	rpc BackendInformation(google.protobuf.Empty) returns (BackendInformationResponse);
+}
+
+message BackendInformationResponse {
+	string id = 1 [(gogoproto.customname) = "ID"];
+}