Add configuration to merge updates automatically

Since we have a CI and we are dealing with a static website
(and no one seems to review the PR anyway besides me), it can safely be
merged, avoiding me 3 clicks on github every day.

.github/workflows/dependabot_automerge.yml

@@ -0,0 +1,16 @@
+name: Auto-merge Dependabot
+on: pull_request
+
+permissions:
+  pull-requests: write
+  contents: write
+
+jobs:
+  automerge:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - uses: peter-evans/enable-pull-request-automerge@v3
+        with:
+          pull-request-number: ${{ github.event.pull_request.number }}
+          merge-method: rebase