chore: Add license headers to all files

testing/controller/docs.go

@@ -1,2 +1,5 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
 // Package controller is a package meant for internal testing only.  The interfaces may change or be removed at any time without warning.
 package controller