Adds Prometheus scrape of Velero's :8085 metrics and four alerts
(VeleroBackupFailed, VeleroBackupPartial, VeleroBackupMissed,
VeleroStorageLocationUnavailable) labeled team=infra severity=warning.
VeleroStorageLocationUnavailable substitutes for the spec's
VeleroRepoUnhealthy since Velero v1.18.1 does not expose
velero_backup_repository_available (see comment in the rule).
Wired via a new ArgoCD Application (velero-monitoring) that syncs
only servicemonitor.yaml + prometheusrule.yaml from basicstack-repo/velero/.
Co-Authored-By: Paperclip <noreply@paperclip.ing>
