ci: enfore changelog entry on PR

Author: tkan145

.github/workflows/changelog-requirement.yml

@@ -0,0 +1,33 @@
+name: Changelog Requirement
+
+on:
+  pull_request:
+    types: [ opened, synchronize, labeled, unlabeled ]
+    paths:
+      - 'gateway/**'
+
+jobs:
+  require-changelog:
+    if: ${{ !contains(github.event.*.labels.*.name, 'skip-changelog') }}
+    name: Requires changelog
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 2
+
+      - name: Find changelog files
+        id: changelog-file
+        uses: tj-actions/changed-files@24d32ffd492484c1d75e0c0b894501ddb9d30d62 # v47
+        with:
+          # Avoid using single or double quotes for multiline patterns
+          files: |
+            CHANGELOG.md
+
+      - name: Check changelog existence
+        if: steps.changelog-file.outputs.any_changed == 'false'
+        run: |
+          echo("Please include a CHANGELOG entry. You can find it at [CHANGELOG.md](https://github.com/3scale/apicast/blob/master/CHANGELOG.md)."
+          echo "Note, we hard-wrap at 80 chars and use 2 spaces after the last line."
+          echo "If you believe this PR requires no changelog entry, label it with \"skip-changelog\"."
+          exit 1