fix(terraform-pipeline): speed up plan jobs with needs relationships

A quick change to the terraform-pipeline.yml after some more testing. Basically, I realised that the recent changes meant that plan jobs no longer run concurently. Instead, they wait for each previous stage to complete, unnecessarily slowing down the pipeline. Also, the deployment pipeline (triggered on merge to the default branch) has a bug in that the staging jobs do not start automatically as they wait for the previous stage which contains the manual development apply job (marked as manual to avoid accidentally trashing other developer's WIP etc.).

The fix is to set some needs relationships so that the plan jobs need all of the test jobs, allowing them to start at the same time regardless of stage.

And also to set the production apply job to need the staging apply job (in addition to the production plan job). This ensures that, even though the production plan job can now start as soon as the tests have completed, the apply still has to wait for a successful deployment to staging before starting.