chore(ci): add pr task list check workflow

relates to STACKITTPR-138

Author: rubenhoenle

.github/workflows/pr-task-list.yaml

@@ -0,0 +1,14 @@
+name: "PR task list check"
+
+on:
+  pull_request:
+    types: [opened, edited, synchronize, reopened]
+
+jobs:
+  task-list-checker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check for incomplete task list items
+        uses: Shopify/task-list-checker@main
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}