add deprecation warning for Vault/Consul token usage

[tgross]

Submitting a Consul or Vault token with a job is deprecated in Nomad 1.7 and intended for removal in Nomad 1.9. Add a deprecation warning to the CLI when the user passes in the appropriate flag or environment variable.

Nomad agents will no longer need a Vault token when configured with workload identity, and we'll ignore Vault tokens in the agent config after Nomad 1.9. Log a warning at agent startup.

Ref: #15617
Ref: #15618

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Resulting log line in the agent:

2023-10-25T10:15:27.664-0400 [WARN] agent: Setting a Vault token in the agent configuration is deprecated and will be removed in Nomad 1.9. Migrate your Vault configuration to use workload identity.: cluster=default

Resulting output from nomad job run:

$ nomad job run -vault-token hvs.RYwFOzaEc8aKyNIMzNiHfi4w ~/ws/nomad/etc/jobs/httpd.nomad
Warning: setting a Vault token when submitting a job is deprecated and will be
removed in Nomad 1.9. Migrate your Vault configuration to use workload identity.
==> 2023-10-25T10:16:19-04:00: Monitoring evaluation "a884a82e"
    2023-10-25T10:16:19-04:00: Evaluation triggered by job "httpd"
    2023-10-25T10:16:20-04:00: Evaluation within deployment: "25cc4819"
    2023-10-25T10:16:20-04:00: Allocation "a4ca7d9b" created: node "7a1e78e3", group "web"
    2023-10-25T10:16:20-04:00: Evaluation status changed: "pending" -> "complete"
==> 2023-10-25T10:16:20-04:00: Evaluation "a884a82e" finished with status "complete"
==> 2023-10-25T10:16:20-04:00: Monitoring deployment "25cc4819"
  ⠇ Deployment "25cc4819" in progress...
  ...