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/metropolis/node/core/abloader/main.rs b/metropolis/node/core/abloader/main.rs
index 905c3ca..4489b73 100644
--- a/metropolis/node/core/abloader/main.rs
+++ b/metropolis/node/core/abloader/main.rs
@@ -1,3 +1,8 @@
+/*
+ * Copyright The Monogon Project Authors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 #![no_main]
 #![no_std]