Backport of CSI: failed allocation should not block its own controller unpublish into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #14484 to be assessed for backporting due to the inclusion of the label backport/1.3.x.

The below text is copied from the body of the original PR.

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A Nomad user reported problems with CSI volumes associated with failed allocations, where the Nomad server did not send a controller unpublish RPC.

The controller unpublish is skipped if other non-terminal allocations on the same node claim the volume. The check has a bug where the allocation belonging to the claim being freed was included in the check incorrectly. During a normal allocation stop for job stop or a new version of the job, the allocation is terminal so that's ok. But allocations that fail are not yet marked terminal at the point in time when the client sends the unpublish RPC to the server.

For CSI plugins that support controller attach/detach, this means that the controller will not be able to detach the volume from the allocation's host and the replacement claim will fail until a GC is run. This changeset fixes the conditional so that the claim's own allocation is not included, and makes the logic easier to read. Include a test case covering this path.

This PR includes two other tiny bug fixes that were going to be a pain if I had to backport 3 different PRs. They're in their own commits:

• Fix missing copies in the volume unpublish workflow. Entities we get from the state store should always be copied before altering. Ensure that we copy the volume in the top-level unpublish workflow before handing off to the steps.
• The list stub object for volumes in nomad/structs did not match the stub object in api. The api package also did not include the current readers/writers fields that are expected by the UI. True up the two objects and add the previously undocumented fields to the docs.

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