Enable auto-sync for bookstack application

Configure Argo CD to automatically sync bookstack from the repository,
ensuring the repository remains the single source of truth.

Changes:
- Added automated sync policy with prune and selfHeal
- prune: removes resources no longer in repo
- selfHeal: reverts manual cluster changes back to repo state

This resolves the manual sync requirement and ensures continuous
synchronization without data loss.

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

apps/app-bookstack.yaml

@@ -13,5 +13,8 @@ spec:
     server: https://kubernetes.default.svc
     namespace: bookstack
   syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
     syncOptions:
     - CreateNamespace=true