Feature Request: Add support for `sensitive-variables`

Packer currently implements a `sensitive-variables` feature that would be very nice in Nomad. Specifically for the Job definition in the UI. It is nice to allow devs and management access to a read-only version of the UI using ACLs but they are not fine grained enough.

I would like to allow access but simple hide secrets that are passed into the job using `env` vars in 12-factor app style.

https://packer.io/docs/templates/user-variables.html

Start with the Job definition in the UI and review the linked Packer user-variables documentation for the intended sensitive-variables behavior. Determine how env vars passed into jobs should be represented for read-only users, with completion defined as hiding secrets while preserving permitted Job visibility.

Written by the indexing model from the issue text.