[FEATURE] Support the metadata variables in a stack definition

[joshuacook-tamu]

Is your feature request related to a problem? Please describe.
If you rename the folder structure in a stack while using the orchestration / dependency management features of terramate, you have to manually update any references.

Describe the solution you'd like
Support the metadata variables in a stack definition, particularly for orchestration (before, after, etc.). This would allow for easy renaming / moving of stack folder structure without having to remember to update config in the stack definition.

Describe alternatives you've considered
I have substituted by directly referencing the name of the path.

Additional context
See bug #692

[katcipis]

@joshuacook-tamu thanks for creating this issue. We are working on other features on our roadmap right now but as soon as we have any news related to this issue we will update it here.