treewide: add license header and enable haslicense linter

Change-Id: I873a8d4082d75e8f813d8a726a41187eea7a065e
Reviewed-on: https://review.monogon.dev/c/monogon/+/3825
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/cloud/agent/takeover/e2e/main_test.go b/cloud/agent/takeover/e2e/main_test.go
index b141e63..9ab6769 100644
--- a/cloud/agent/takeover/e2e/main_test.go
+++ b/cloud/agent/takeover/e2e/main_test.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package e2e
 
 import (
diff --git a/cloud/agent/takeover/takeover.go b/cloud/agent/takeover/takeover.go
index bf7760c..9af4872 100644
--- a/cloud/agent/takeover/takeover.go
+++ b/cloud/agent/takeover/takeover.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 // takeover is a self-contained executable which when executed loads the BMaaS
 // agent via kexec. It is intended to be called over SSH, given a binary
 // TakeoverInit message over standard input and (if all preparation work