Docs: Add manage Nomad variables page

[aimeeu]

Description

• Add a new page on how to create, update, delete, and lock Nomad variables. This replaces the navigation link to the page in tutorials. I left the Nomad variables pages in the tutorial repo and linked to them. We can revisit in 6 months to see if people are still accessing those tutorials.
• Pull CLI examples into partials, update, and use in new page and CLI command reference.

Links

Jira: CE-974

https://nomad-git-ce974vars-hashicorp.vercel.app/nomad/docs/manage/manage-variables

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad website documentation to reflect this. Refer to
  the website README for docs guidelines. Please also consider whether the
  change requires notes within the upgrade guide.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

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[boruszak]

Great work.

All I have is little nits. Including this request: Can you change manage/manage-variables.mdx to manage/variables.mdx to simplify the path?

[boruszak]

Suggested change

	Most Nomad workloads need access to configuration values or secrets. Nomad has a
	`template` block to [provide such configuration to
	tasks](/nomad/docs/job-specification/template#nomad-variables). Nomad variables
	provide the option to store configuration at file-like paths
	directly in Nomad's state store. Access these variables directly from
	your task templates. Nomad encrypts and replicates the contents of these variables between servers via Raft. Access to variables is controlled by
	Most Nomad workloads need access to configuration values or secrets. Nomad has a
	`template` block to [provide these values to
	tasks](/nomad/docs/job-specification/template#nomad-variables). Nomad variables
	provide the option to store configuration at file-like paths
	directly in Nomad's state store so that you can access these variables directly from
	your task templates. Nomad encrypts and replicates the contents of these variables between servers with Raft communication. Access to variables is controlled by

[boruszak]

Suggested change

	Nomad scopes a Nomad variable to a namespace. You may control access to Nomad
	variables with ACL policies.
	Nomad scopes a Nomad variable to a namespace and allows access to Nomad
	variables according to ACL policies.

[boruszak]

Suggested change

	To learn how to access Nomad variables in your job specification, refer to the
	[Use Nomad variables in tasks](/nomad/docs/job-declare/nomad-variables) guide.
	To learn how to access Nomad variables in your job specification, refer to [Use Nomad variables in tasks](/nomad/docs/job-declare/nomad-variables).

[boruszak]

Suggested change

	Use a hyphen ("-") to instruct the command to read the variable value from
	Use a hyphen (`-`) to instruct the command to read the variable value from