Backport of Add stage_publish_dir field to csi_plugin stanza of a job into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #13919 to be assessed for backporting due to the inclusion of the label backport/1.3.x.

WARNING automatic cherry-pick of commits failed. Commits will require human attention.

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

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Resolves #13263.

This PR adds a new field to the csi_plugin stanza of a job that determines the base (inside a CSI plugin's container) of CSI staging_target_path and target_path directories.

This is my first PR to Nomad. I have attempted to go through the bullets in the checklist below. Some of the bullets are (I think) not applicable. For the docs, I tried to find all locations within /docs where CSI is mentioned and add the field as appropriate.

I updated comments on a couple of fields that I found to be confusing while trying to figure out where and how to get this implemented. I'm obviously open to reverting anything that the maintainers think is not an improvement.

Code

• Consider similar features in Consul, Kubernetes, and other tools. Is there prior art we should match? Terminology, structure, etc?
• Add structs/fields to api/ package
  • api/ structs usually have Canonicalize and Copy methods
  • New fields should be added to existing Canonicalize, Copy methods
  • Test the structs/fields via methods mentioned above
• Add structs/fields to nomad/structs package
  • structs/ structs usually have Copy, Equals, and Validate methods
  • Validation happens in this package and must be implemented
  • Note that analogous struct field names should match with api/ package
  • Test the structs/fields via methods mentioned above
  • Implement and test other logical methods
• Add conversion between api/ and nomad/structs/ in command/agent/job_endpoint.go
  • Add test for conversion
• Determine JSON encoding strategy for responses from RPC (see "JSON Encoding" below)
  • Write nomad/structs/ to api/ conversions if necessary and write tests
• Implement diff logic for new structs/fields in nomad/structs/diff.go
  • Note that fields must be listed in alphabetical order in FieldDiff slices in nomad/structs/diff_test.go
  • Add test for diff of new structs/fields
• Add change detection for new structs/fields in scheduler/util.go/tasksUpdated
  • Might be covered by .Equals but might not be, check.
  • Should return true if the task must be replaced as a result of the change.

Docs

• Changelog
• Jobspec entry https://www.nomadproject.io/docs/job-specification/index.html
• Jobspec sidebar entry https://github.com/hashicorp/nomad/blob/main/website/data/docs-navigation.js
• Job JSON API entry https://www.nomadproject.io/api/json-jobs.html
• Sample Response output in API https://www.nomadproject.io/api/jobs.html
• Consider if it needs a guide https://www.nomadproject.io/guides/index.html

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[tgross]

Already backported in #13965

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