feat(aula-17): adicionar Cloud Native PostgreSQL (CNPG)

- Cluster PostgreSQL 3 instâncias com anti-affinity por hostname (hard)
  e por zona (soft) para spread entre datacenters Hetzner
- Backup automático via Barman Cloud para Hetzner Object Storage (S3)
- ScheduledBackup diário às 03:00
- App demo que valida conexão com o banco
- setup.sh: instala operator, cria cluster, deploya demo
- cleanup.sh: remoção limpa (backups S3 preservados)

aula-17/cnpg/scheduled-backup.yaml

@@ -0,0 +1,11 @@
+apiVersion: postgresql.cnpg.io/v1
+kind: ScheduledBackup
+metadata:
+  name: shared-postgres-backup
+  namespace: cnpg
+spec:
+  cluster:
+    name: shared-postgres
+  schedule: "0 3 * * *"
+  backupOwnerReference: cluster
+  method: barmanObjectStore