CSI: updates on register/create aren't allowed

[tgross]

While working on #10927 and #10833 and I noticed that csi_hook.go doesn't implement interfaces.RunnerUpdateHook, so there's no way to update CSI volume in place on an allocation, but the validateJobUpdate doesn't know that and will merrily let you update it without warning you.

Implement the RunnerUpdateHook interface as well.

[tgross]

After having spent some time in the register/create workflow to do #12129 I'm realizing that we generally can't implement CSI hooks non-destructively, because all the client-side behaviors would require remounting the volume. So there's no need for an update hook in csi_hook.go.

But we do need to make sure the semantics of updating a volume with nomad volume register and nomad volume create are correct and legible. I'm going to update the title of this issue for that instead.

[github-actions]

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