Add CI to require labels on PRs for better changelog management (matrix-org#2337)

Author: t3chguy

.github/workflows/preview_changelog.yaml

@@ -0,0 +1,24 @@
+name: Pull Request
+on:
+  pull_request_target:
+    types: [ opened, edited, labeled, unlabeled ]
+jobs:
+  changelog:
+    name: Preview Changelog
+    runs-on: ubuntu-latest
+    steps:
+      - uses: matrix-org/allchange@main
+        with:
+          ghToken: ${{ secrets.GITHUB_TOKEN }}
+
+  enforce-label:
+    name: Enforce Labels
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: read
+    steps:
+      - uses: yogevbd/[email protected]
+        with:
+          REQUIRED_LABELS_ANY: "T-Defect,T-Deprecation,T-Enhancement,T-Task"
+          BANNED_LABELS: "X-Blocked"
+          BANNED_LABELS_DESCRIPTION: "Preventing merge whilst PR is marked blocked!"