Make mostly reuse conformant (#502)

* Add .license files.

* Update README.

* Normalize licenses test.

* Add reuse GHA.

* Add blanket rule for changelog fragments.

* Add .license file for vendored third-party certificates.

* Fix workflow's permissions.

* Revert "Add .license file for vendored third-party certificates."

This reverts commit 35e106867c.

* Make reuse lint test optional.

* Add exceptions.

* Update README.

* Improve reuse test.

.github/workflows/reuse.yml

@@ -0,0 +1,34 @@
+---
+# Copyright (c) Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+name: Verify REUSE
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  # Run CI once per day (at 04:45 UTC)
+  schedule:
+    - cron: '45 4 * * *'
+
+jobs:
+  check:
+    permissions:
+      contents: read
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install dependencies
+        run: |
+          pip install reuse
+
+      - name: Check REUSE compliance (except some PEM files)
+        run: |
+          rm -f tests/integration/targets/*/files/*.pem
+          rm -f tests/integration/targets/*/files/roots/*.pem
+          reuse lint