Backport of docs: create volume spec page into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #13353 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.

---

In addition to jobs, there are other objects in Nomad that have a
specific format and can be provided to commands and API endpoints.

This commit creates a new menu section to hold the specification for
volumes and update the command pages to point to the new centralized
definition.

Redirecting the previous entries is not possible with redirect.js
because they are done server-side and URL fragments are not accessible
to detect a match. So we provide hidden anchors with a link to the new
page to guide users towards the new documentation.

Backporting will need to be done manually as not all moved content applies to all versions.

Preview link: https://nomad-b9yy9521h-hashicorp.vercel.app/docs/other-specifications/volume

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