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/build/analysis/importsort/classify.go b/build/analysis/importsort/classify.go
index dc5c45d..88d425e 100644
--- a/build/analysis/importsort/classify.go
+++ b/build/analysis/importsort/classify.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package importsort
 
 import (
diff --git a/build/analysis/importsort/importsort.go b/build/analysis/importsort/importsort.go
index 1b33b3b..6620a04 100644
--- a/build/analysis/importsort/importsort.go
+++ b/build/analysis/importsort/importsort.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 // importsort implements import grouping style checks as per
 // CODING_STANDARDS.md.
 package importsort
diff --git a/build/analysis/importsort/importsort_test.go b/build/analysis/importsort/importsort_test.go
index 723e7d2..2ad2465 100644
--- a/build/analysis/importsort/importsort_test.go
+++ b/build/analysis/importsort/importsort_test.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package importsort
 
 import (