Backport of docs: clarify requirements for Consul token policies and TTLs into release/1.7.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #24167 to be assessed for backporting due to the inclusion of the label backport/1.7.x.

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

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As of #24166, Nomad agents will use their own token to deregister services and checks from Consul. This returns the deregistration path to the pre-Workload Identity workflow. Expand the documentation to make clear why certain ACL policies are required for clients.

Additionally, we did not explicitly call out that auth methods should not set an expiration on Consul tokens. Nomad does not have a facility to refresh these tokens if they expire. Even if Nomad could, there's no way to re-inject them into Envoy sidecars for Consul Service Mesh without recreating the task anyways, which is what happens today. Warn users that they should not set an expiration.

Closes: #20185 (wontfix)
Ref: https://hashicorp.atlassian.net/browse/NET-10262

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Overview of commits

• 7381f84

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