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/bmaas/bmdb/bmdb.go b/cloud/bmaas/bmdb/bmdb.go
index 242c3d9..400aa4a 100644
--- a/cloud/bmaas/bmdb/bmdb.go
+++ b/cloud/bmaas/bmdb/bmdb.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 // Package bmdb implements a connector to the Bare Metal Database, which is the
 // main data store backing information about bare metal machines.
 //