feat: Add job that removes old workflow runs

/kind feat
/area ci

Add script and schedule workflow that removes workflow runs older than specific threshold.

Workflow runs every night at 0:11 UTC and removes up to 500 runs at a time.

.github/workflows/ci-cleanup-workflows.yaml

@@ -0,0 +1,21 @@
+on:
+  schedule:
+    - "11 0 * * *"
+
+permissions:
+  actions: write
+
+jobs:
+  cleanup:
+    runs-on: ubuntu-latest
+    steps:
+      - id: cleanup
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          AFTER: "14d"
+          LIMIT: 500
+        run: |
+          DATE="$(date -uI -v -$AFTER)"
+          echo "Removing workflow runs older than $AFTER..."
+          gh run list --json databaseId -q '.[].databaseId' --created "<=$DATE" --limit "$LIMIT" | \
+            xargs -IID gh run delete ID