ci: add changelog enforcement

.github/workflows/changelog.yml

@@ -0,0 +1,18 @@
+name: "Check CHANGELOG.md"
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, ready_for_review, labeled, unlabeled]
+    paths-ignore:
+      - "docs/colang-2"
+      - "nemoguardrails/colang/v2_x"
+      - "cli"
+
+jobs:
+  # Enforces the update of a changelog file on every pull request
+  changelog:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dangoslen/changelog-enforcer@v2
+        with:
+          changeLogPath: "CHANGELOG.md"