Re-use workflows

[softius]

Given that we already have named workflows, we can implement a jump functionality so that another workflow will be executed. This will allow to re-use workflows.

$workflow->to('my-unique-id');

It might be necessary to convert exchanges between the parent workflow.

$workflow
  ->callback(function() {
    // Convert exchange
  })
  ->to('my-unique-id');

When the sub-workflow is completed, we will need to revert to the original Exchange.