misc: add reusable changelog-verification action (#93)

Author: lauzadis

.github/actions/changelog-verification/action.yml

@@ -0,0 +1,31 @@
+name: 'Changelog Verification'
+description: 'Verifies that a PR includes a valid changelog entry'
+
+runs:
+  using: "composite"
+  steps:
+    - name: Checkout sources
+      uses: actions/checkout@v4
+
+    - name: Setup kat
+      uses: awslabs/aws-kotlin-repo-tools/.github/actions/setup-kat@main
+
+    - name: Check for new changelog entry
+      if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-changelog') }}
+      shell: bash
+      run: |
+        git fetch origin ${{ github.base_ref }} --depth 1
+        if ! git diff remotes/origin/${{ github.base_ref }} --name-only | grep -P "\.changes/[0-9a-f-]+\.json"; then
+          echo "::error ::No new/updated changelog entry found in /.changes directory. Please either:"
+          echo "::error ::* Add a changelog entry (see CONTRIBUTING.md for instructions) or"
+          echo "::error ::* Add the 'no-changelog' label to this PR (in rare cases not warranting a changelog entry)"
+          exit 1
+        fi
+
+    - name: Verify all changelogs
+      shell: bash
+      run: |
+        if ! kat changelog ls; then
+          echo "::error ::Changelog verification failed. Please check the format of your changelog entry."
+          exit 1
+        fi