Add CNPG ScheduledBackup for authentik/n8n/nextcloud - WAL archiving alone isn't restorable

Found while building the VPS replica clusters (Phase 2): all three
CNPG clusters' backup.barmanObjectStore blocks only configure continuous
WAL archiving. CNPG's bootstrap.recovery needs at least one real Backup
object in the object store before it has anything to restore -
'no target backup found', confirmed live against pg-authentik. This gap
was systemic (gitlab has it too, not fixed here - out of scope for
tonight, no VPS standby depends on it).

immediate: true fires one backup right away in addition to the daily
01:00 schedule, to unblock the in-progress VPS restore now rather than
waiting up to 24h for the first scheduled run.

apps/nextcloud/manifests/scheduled-backup.yaml

@@ -0,0 +1,16 @@
+---
+# Same gap/fix as infrastructure/authentik/manifests/scheduled-backup.yaml -
+# see that file for the full explanation. WAL-only barmanObjectStore
+# config has no restorable base backup without this.
+apiVersion: postgresql.cnpg.io/v1
+kind: ScheduledBackup
+metadata:
+  name: pg-nextcloud-backup
+  namespace: nextcloud
+spec:
+  schedule: "0 1 * * *"
+  backupOwnerReference: self
+  immediate: true
+  method: barmanObjectStore
+  cluster:
+    name: pg-nextcloud