When we add a Sentinel scope for dynamic host volumes, having a default `-scope`
value for `sentinel apply` risks accidentally adding policies for volumes to the
job scope. This would immediately prevent any job from being submitted. Forcing
the administrator to pass a `-scope` will prevent accidental misuse.
Ref: https://github.com/hashicorp/nomad-enterprise/pull/2087
Ref: https://github.com/hashicorp/nomad/pull/24479
