Add support for configuring rclone retries in backup container

[David-Igou]

Currently, in the helm-chart, the backup container is ran as a sidecar. This creates a scenario where if the S3 endpoint becomes unavailable for whatever reason, the pod frequently restarts and essentially creates a server outage.

This can be mitigated by having the mc-backup able to be configured to indefinitely retry the rclone sync without exiting with a failure, if so the user chooses.

[itzg]

Good idea!