Backup: Adding CSI Snapshot support

[ricsanfre]

Enhancement Request

Enabling within K3S cluster the new Kubernetes CSI feature: Volume Snapshots to be able to programmatically create backups and so orchestrate consistent backups:

   kubectl exec pod -- app_feeze_command
   kubectl apply -f volume_snapshot.yml
   # wait till snapshot finish
   kubectl exec pod -- app_unfreeze_command

Implementation details

CSI Snapshot feature is supported by Longhorn. See Longhorn documentation: CSI Snapshot Support. K3S currently does not come with a preintegrated Snapshot Controller, but external controller could be used (https://github.com/kubernetes-csi/external-snapshotter).

[ricsanfre]

Additional feature

Congigure Velero to use CSI Snapshots. Velero CSI Snapshots documentation

See this longhorn discussion for implementation details longhorn/longhorn#3731

[ricsanfre]

Enabling Velero CSI snapshots requires to deploy velero-plugin-for-csi

Currently, velero-plugin-for-csi docker image is not supporting arm64 architecture.

There is an open issue vmware-tanzu/velero#4303 and PR which fixes it: vmware-tanzu/velero-plugin-for-csi#116