Configurable migrate job image and disable migration resources if persisted identity exists

[rndmit]

This PR makes it possible to override the migration job image and fixes the unnecessary creation of migration resources (such as PVC) if the identity is set by .Values.secret.existingSecretName

[qrkourier]

Out of curiosity, is portainer/kubectl-shell a superior image in general, or specifically for this scenario, than bitnami/kubectl, or preferred for some other reason? I'm not strongly opinionated and hope to gain your insight on this.

[rndmit]

It's actually not. But it was the first one I found with bash installed.
And if your question is about "why it was changed?" - because of this: bitnami/containers#83267 (tldr; bitnami catalog will be deprecated soon)

[qrkourier]

This reminded me about a problem report: #338

The solution is to refactor the ZET chart (the node proxy daemonset) to delete the migration job, which is no longer relevant, clarify the two deployment modes (identity in writable PVC vs. existing read-only secret), and stop hard-coding the PVC access mode, since it must be RWX if there's more than one cluster worker node. Pull request on-the-way.

[rndmit]

Hello again,
Just wanted to ask: how soon will it be ready?
There is no more bitnami/kubectl:latest image. So, the current version of chart is not working.

[qrkourier]

@rndmit Since the ZET 1.2.0 chart was broken when Bitnami decommissioned the kubectl image, I have released the ZET 1.3.0 chart immediately and will begin testing. Please raise a GH issue if you find a problem.