arrstack: run sonarr/radarr/prowlarr active-active on shared Postgres (#arrstack)

Convert the three *arr apps from single-replica upstream LinuxServer/SQLite to
our -unkin2 forks running active-active (replicas 3) on a shared CNPG Postgres
cluster.

- new apps/base/arrstack/postgres/: CNPG Cluster arrstack-postgres (3 instances,
  3 managed login roles sonarr/radarr/prowlarr, throwaway initdb owner), per-app
  Database CRDs (<app>-main), cephrgw backup bucket + nightly ScheduledBackup,
  and 3 VaultStaticSecrets syncing the <app>-db role credentials.
- per app: image -> docker-internal/<app>:v<base>-unkin2; replicas 3 +
  RollingUpdate; drop the apikey-init initContainer + PUID/PGID/TZ; run the
  binary directly with -nosingleinstancecheck; env from a new ConfigMap plus
  Postgres user/password and the API key from Secrets; /config PVC -> RWX
  cephfs-raid5-retain (shared).

apps/base/arrstack/radarr/kustomization.yaml

@@ -5,6 +5,7 @@ kind: Kustomization
 resources:
   - pvc-config.yaml
   - vaultstaticsecret.yaml
+  - configmap.yaml
   - deployment.yaml
   - service.yaml
   - gateway.yaml