Feature - add the local clients advertise address to interpolation env vars

[jrasell]

In some situations, Nomad tasks need to communicate to the Nomad API. Currently there is no interpolation environment variable which allows the local Nomad clients advertise address to be passed to the task for use making calls. It would be super helpful if NOMAD_ADVERTISE_ADDR or similar could be added for this task.

[github-actions]

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