Improve config package names and reduce API exposure.

api/konfig/builtinpluginconsts/doc.go

@@ -0,0 +1,8 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package builtinpluginconsts provides builtin plugin
+// configuration data.  Builtin plugins can also be
+// configured individually with plugin config files,
+// in which case the constants in this package are ignored.
+package builtinpluginconsts