feat: add auto-update versions workflow

The new workflow added in `.github/workflows/auto-update-versions.yml` takes care of automatically updating the Vespa version in the project's documentation. The workflow is triggered either manually or on a daily schedule, and it fetches the latest Vespa version from the Maven repository and updates the relevant files in the repository.

.github/workflows/auto-update-versions.yml

@@ -0,0 +1,33 @@
+name: Auto-update versions
+#
+#  Takes care of updating the Vespa version in the documentation.
+#
+
+on:
+  workflow_dispatch: # Allow manual triggering of the workflow
+
+  schedule:
+    - cron: "0 0 * * *"
+
+  # For testing purposes
+  push:
+    branches: [auto-update-versions]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  update-vespa-version:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Get Latest Vespa version
+        run: |
+          VESPA_VERSION=$(curl -sSL https://repo1.maven.org/maven2/com/yahoo/vespa/parent/maven-metadata.xml | \
+            grep -oP '<latest>\K([0-9]+\.[0-9]+\.[0-9]+)')
+
+          xq --version
+          echo "Vespa version: $VESPA_VERSION"