[Refactor] Internalize konfig constants

This PR is an effort towards internalizing public APIs.
It moves some of the builtinconstants to internal/

Signed-off-by: Varsha Prasad Narsing <varshaprasad96@gmail.com>

api/internal/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