Add license header to new failpoint.go

Author: matthewdale

internal/failpoint/failpoint.go

@@ -1,3 +1,9 @@
+// Copyright (C) MongoDB, Inc. 2024-present.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
 package failpoint
 
 import (