[feature] way to know if plan is going to cause any changes from the cli

[camerondavison]

currently when a plan is run for a job, it is very pretty for humans to look at but somewhat hard to figure out if anything is going to change from the command through the cli.

One simple fix for this would be to have the return code be either

• 0 nothing is going to happen
• 1 something is going to change
• 130 or something else (error contacting nomad)

[github-actions]

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