Create manual backup

Triggering a manual backup can be done like this:

cat <<EOF | kubectl apply -f-
apiVersion: pxc.percona.com/v1
kind: PerconaXtraDBClusterBackup
metadata:
  name: manual
  namespace: syseleven-pxc-operator
spec:
  pxcCluster: pxc-db
  storageName: s3
EOF