Support parallel deployments to multiple regions with an environment but still present the deployment diff dialog

We have multiple 'regions' within each environment.

For speed in deployment we have a Pipelines step that is manually triggered and will then deploy to all the regions in parallel, using a parallel step.

The problem with this approach is that all the deployment steps are nested within a 'parallel' and therefore BBP will not display the diff dialog showing the issues and commits that are going to be deployed.  We miss the assurance/safety that this dialog offers.

It would be great if we could have some kind of 'parallel deployment' step that would still show this diff dialog. So the requirements are:

1. Manually triggered parallel deployment to multiple 'regions' within an environment (staging and production)
2. Presentation of the 'environment diff' dialog before these deployments.
   1. we maintain all regions within an environment at the same deployment but I understand there would be complexities if these regions were out of sync.

At the moment we can 'emulate' the above by creating a 'fake environment' and we use this in the deployment step that then triggers the parallel deployment to the real environments

e.g.

 
<snip>
# Manually trigger deployment to a non-real first stg region, then the rest will trigger in parallel automatically.
# This is so BBP can still show us the deployment diff dialog which you lose if you parallel up all the deployments.
- step:name: Deploy to stg environments
  deployment: stg-null
  <<: *null-deploy-for-kickoff
  - parallel:
  - step:
      name: Deploy service to stg-env-1
      deployment: stg-env-1
      <<: *service-deploy
  - step:
      name: Deploy service{{ to stg-env-2}}
      deployment: stg-env-2
      <<: *service-deploy
  - step:
      name: Deploy service{{ to stg-env-3}}
      deployment: stg-env-3
      <<: *service-deploy
<etc>