Add a daily 03:15 UTC restic backup of the grafana-storage PVC to
s3:${S3_ENDPOINT}/${S3_BUCKET}/restic/grafana. Pinned to
k3s-worker-2 via nodeSelector because grafana-storage is a
local-path PV anchored there — no podAffinity needed. Same restic
retention as the loki sibling (7d/4w/6m + prune + 5% check) with
metrics backup_grafana_{success,timestamp_seconds,check_status}
written to the emptyDir textfile path. Deployed in parallel with
the legacy backup-volumes CronJob (Option 4 rollout, DEV-482).
Co-Authored-By: Paperclip <noreply@paperclip.ing>
