Add a concrete example on how to restore a cert-manager installation

[inteon]

The /docs/devops-tips/backup page was already describing how to backup using Velero.
However, there was no concrete example that shows how to do this.
This PR adds that example (including a workaround to properly restore the owner reference on a Certificate created by ingress-shim).

You can use Velero locally using these commands (see https://velero.io/docs/v1.12/contributions/minio/):

kubectl apply --server-side -f ./examples/minio/00-minio-deployment.yaml

./velero install \
    --provider aws \
    --plugins velero/velero-plugin-for-aws:v1.2.1 \
    --bucket velero \
    --secret-file ./credentials-velero \
    --use-volume-snapshots=false \
    --backup-location-config region=minio,s3ForcePathStyle="true",s3Url=http://minio.velero.svc:9000

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[wallrj]

Thanks @inteon

It's interesting to see some examples of how to use the velero CLI.

I was surprised that the instructions recommend restoring the cert-manager app in the same phase as the custom resources.
My expectation was that the cert-manager app would be excluded from the backup, because it can so easily be re-installed from the Helm chart or manifests.
Or else that cert-manager (and other platform apps) would be backed up and restored separately from the applications that run on the platform.
But I have no idea how people actually use Velero.

Perhaps this will trigger some reactions from our users, who can refine the instructions with their real world experiences.

I found a couple of related issues:

• In Docs for controller developers  vmware-tanzu/velero#6799, @guettli requests documentation which will help us answer some of these questions.
• In restore with object metadata.ownerreference and metadata.finalizer vmware-tanzu/velero#4707, @polym requests that Velero allow backing up and restoring owner refs, which might help with the Ingress > Certificate ordering problems.

/lgtm
/hold because I think we should remove the word "recommend"

[wallrj]

Great.

/lgtm

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[inteon]

/unhold