Make new nesting place for generated builtin code.

api/plugins/builtinconfig/doc.go

@@ -0,0 +1,8 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package builtinconfig provides legacy methods for
+// configuring builting plugins from a common config file.
+// It's better to configure them individually if using
+// a custom configuration.
+package builtinconfig