Add self-hosted Renovate runner workflow

Creates .github/workflows/renovate.yaml using renovatebot/github-action
with a GitHub App token on a weekly schedule. Extends the shared
 renovate-config from the privilegedescalation/.github repository.

Part of PRI-413

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/renovate.yaml

@@ -0,0 +1,20 @@
+name: Renovate
+on:
+  schedule:
+    - cron: '0 3 * * 0'
+  workflow_dispatch:
+jobs:
+  renovate:
+    runs-on: runners-privilegedescalation
+    steps:
+      - uses: actions/checkout@v4
+      - name: Generate GitHub App token
+        id: app-token
+        uses: actions/create-github-app-token@v3
+        with:
+          app-id: ${{ secrets.RELEASE_APP_ID }}
+          private-key: ${{ secrets.RELEASE_APP_PRIVATE_KEY }}
+      - uses: renovatebot/github-action@v40.3.0
+        with:
+          token: ${{ steps.app-token.outputs.token }}
+          configurationFile: renovate.json