[FEATURE/DOCS] Properly handle model group deletion

[dbwiddis]

Is your feature request related to a problem?

Users can use the ModelGroup step to create a model group, but there's no corresponding deletion. However, the documentation indicates that a model group is automatically deleted when the last model in it is deleted (and you can't delete it until then).

There appears to be an edge case of creating a model group (empty) and then wanting to delete it, but this seems an extremely unlikely scenario to encounter in a workflow environment.

What solution would you like?

Pick one:

1. add a workflow step to delete a model group, recognizing it will often return a deletion status of "not found". (May be preferable for easier tracking of removing the resource id)
2. update the deprovision workflow to use the "noop" step to "deprovision" a model group (probably just a quick change in the WorkflowResources enum). (May be preferable if we just want to remove the resource id anyway.)