Add S3 backups to all CNPG Postgres clusters

None of the CNPG clusters had any backup configured, so a lost PVC or a bad
migration meant permanent data loss. This adds continuous WAL archiving plus a
nightly base backup to Ceph RGW for every cluster, with restore docs.

- Add spec.backup.barmanObjectStore (in-tree; operator is CNPG 1.28, Barman
  Cloud Plugin not deployed) to each cnpg_cluster.yaml: WAL zstd, base bzip2,
  30-day retention, endpointCA via the reflected vault-ca-cert.
- Add cnpg_backup.yaml per app: a cephrgw ObjectStoreUser + Bucket (one
  dedicated s3://cnpg-<app> bucket and owner user per cluster, since cephrgw CRs
  and the CNPG credential Secret are namespace-scoped) and a staggered nightly
  ScheduledBackup. Credentials are minted by the operator; nothing is hardcoded.
- Add the three ceph.unkin.net CRD schemas so kubeconform can validate the CRs.
- Add docs/ (README index, cnpg-backups.md, cnpg-restore.md) covering config and
  full/PITR restore procedures.

Claude-Session: https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv

apps/base/puppet/cnpg_cluster.yaml

@@ -7,6 +7,35 @@ metadata:
 spec:
   affinity:
     podAntiAffinityType: preferred
+  backup:
+    # 30-day retention (DEFAULT — adjust per cluster if needed). Enforced by CNPG
+    # against the object store on each successful base backup.
+    retentionPolicy: 30d
+    barmanObjectStore:
+      # Dedicated per-cluster Ceph RGW bucket (cephrgw-operator provisions it).
+      destinationPath: s3://cnpg-puppet
+      endpointURL: https://s3.ceph.unkin.net
+      # radosgw serves a Vault-PKI cert; trust the internal CA (reflected into
+      # every namespace as the vault-ca-cert Secret).
+      endpointCA:
+        name: vault-ca-cert
+        key: ca.crt
+      # Keys minted by the ObjectStoreUser in cnpg_backup.yaml; never hardcoded.
+      s3Credentials:
+        accessKeyId:
+          name: cnpg-puppet-backup-s3
+          key: AWS_ACCESS_KEY_ID
+        secretAccessKey:
+          name: cnpg-puppet-backup-s3
+          key: AWS_SECRET_ACCESS_KEY
+      # Path prefix within the bucket; keep stable across restores (see docs).
+      serverName: puppet
+      data:
+        compression: bzip2
+        jobs: 2
+      wal:
+        compression: zstd
+        maxParallel: 2
   bootstrap:
     initdb:
       database: puppetdb