Prune old VolumeSnapshots during replication destination reconciliation

[ELENAGER]

Fixes: https://issues.redhat.com/browse/DFBUGS-990

Volsync is leaving behind one snapshot per failover/relocate action, and it causes severe memory problems. The solution is to prune old VolumeSnapshots upon reconciliation of replication destination and leave only one latest VolumeSnapshot, deleting older ones.

[BenamarMk]

(nit) It would be nice to extract this block and the one below into a reusable utility function that deletes a given list of objects. We are deleting a list of snapshots in two different places, one with n-1 items and the other with n items.

ramen/internal/controller/volsync/vshandler.go

Lines 1125 to 1137 in ca44e13

	for i := range snapList.Items {
	snapshot := snapList.Items[i]
	if err := v.client.Delete(v.ctx, &snapshot); err != nil {
	if !errors.IsNotFound(err) {
	v.log.Error(err, "Error cleaning up VolumeSnapshot", "name", snapshot.GetName())
	return err
	}
	}
	v.log.Info("Deleted VolumeSnapshot", "name", snapshot.GetName())
	}

[ELENAGER]

Helper function for deletion of snapshot list added, no more duplicated code.