Is your feature request related to a problem? Please describe.
Currently, running terramate list --run-order gives us a list of stacks sorted by their execution order.

Could you enhance the command to also provide extra details? Specifically, it would be helpful to see groups that need to be executed in sequence, and within each group, identify which stacks can be executed in parallel.

Describe the solution you'd like
instead of this output

stack/app-1
stack/app-2
stack/app-3
stack/app-4

Something like this will be much more helpful

{
  "1": [
    "stack/app-1"
  ],
  "2": [
    "stack/app-2",
    "stack/app-3"
  ],
  "3": [
    "stack/app-4"
  ]
}

Describe alternatives you've considered
NA

Additional context
NA