Make Hail dry-run functionality more accessible

[MattWellie]

It's non-trivial to 'dry-run' a pipeline. The main.py --dry-run functionality is very limited, and just prints the stages in the workflow, +/- some first/last/skipping through config

What I really want to test locally is the code in queue_jobs and expected_outputs, as well as the interconnection between stages. This requires me to run the workflow locally, without the --dry_run parameter (so that the Stage code, expected_outputs, queue_jobs actually runs), but with dry run communicated directly to Hail here through config, to prevent launching of the assembled jobs. To do this (AFAIK) I need to run the pipeline normally (without dry-run), and with a substitute config block like this:

dataset_gcp_project = "test-analysis-dataset-1234"
sequencing_type = "genome"
path_scheme = "local"
driver_image = "<stub>"

[hail]
billing_project = "test-billing-project"
delete_scratch_on_exit = true
dry_run = true
backend = "local"

It would be nice if this was a behaviour I could trigger with just a CLI setting.

Another glitch here is that even providing these config settings, some methods write directly to GCP during workflow setup (e.g. here or here - the latter responds to workflow.dry_run in config, which is a third different place we can add dry_run, and affects a different subset of behaviours.)

[MattWellie]

I feel like this is a cpg-flow User Experience request, rather than a Prod Pipes request... Maybe consolidating down to a single consistent dry_run value, and a way to decorate methods with @inactivate_on_dry_run if they run actual writing during workflow setup?