Tool to help with migration of multiple/all secrets to a new cluster

Some users need to migrate their workload to another cluster.
The set of all the manifests of their workload include all the SealedSecret manifests.

Commonly people simply copy the sealed-secret's controller sealing key(s) into another cluster (e.g. following the backup/restore procedures in our docs) and call it a day.

Copying private keys around is a great way to increase your chances of leaking your private key.

There may be a better way: we could create a _tool_ that performs the same task that `kubeseal --re-encrypt` but by using an arbitrary public key (the one of the target cluster) and in a way that is amenable to be operated in bulk.

Start by reading the existing `kubeseal --re-encrypt` behavior and the backup/restore procedures referenced in the issue, then examine how workload manifests and SealedSecret manifests are handled. Done means a tool can bulk re-encrypt those manifests with a target cluster's public key without copying private sealing keys; no implementation files or tests are named.

Written by the indexing model from the issue text.