Add support for .krmignore file

kyaml/ext/ext.go

@@ -0,0 +1,10 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package ext
+
+// GetIgnoreFileName returns the name for ignore files in
+// packages. It can be overridden by tools using this library.
+var GetIgnoreFileName = func() string {
+	return ".krmignore"
+}