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/go/logging/backend.go b/go/logging/backend.go
index 2fe4556..19c1bab 100644
--- a/go/logging/backend.go
+++ b/go/logging/backend.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package logging
 
 import (
diff --git a/go/logging/leveled.go b/go/logging/leveled.go
index a32b62d..45dfc14 100644
--- a/go/logging/leveled.go
+++ b/go/logging/leveled.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package logging
 
 // Leveled is a generic interface for glog-style logging. There are four