Added estimate billing script for GCP batch runs

[ldhtnp]

I added a script gb_estimate_billing.py that can be used for estimating the cost of runs performed with GCP batch. The script is very similar to estimate_billing.py with a few small changes related to the different metadata structure generated with GCP.

[malachig]

I did a test with preemptible nodes turned on (using Cromwell 87, but the old backend instead of GCP batch). I got this error:

[ERROR] germlineExomeHlaTyping.phlat has not completed running, cost cannot be calculated
Traceback (most recent call last):
  File "/home/mgriffit/git/cloud-workflows/scripts/gb_estimate_billing.py", line 260, in <module>
    cost = get_workflow_cost(args.metadata_dir.rstrip('/'), args.workflow_id)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/mgriffit/git/cloud-workflows/scripts/gb_estimate_billing.py", line 225, in get_workflow_cost
    call_costs[ck] = get_workflow_cost(metadata_dir, call[SUBWORKFLOW_KEY])
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/mgriffit/git/cloud-workflows/scripts/gb_estimate_billing.py", line 222, in get_workflow_cost
    if is_cached_task(call):
       ^^^^^^^^^^^^^^^^^^^^
  File "/home/mgriffit/git/cloud-workflows/scripts/gb_estimate_billing.py", line 73, in is_cached_task
    return call[CACHED_KEY]["hit"] == True
           ~~~~~~~~~~~~~~~~^^^^^^^
KeyError: 'hit'

To reproduce the error:

cd /storage1/fs1/gillandersw/Active/Project_0001_Clinical_Trials/pancreas_leidos/analysis/TWJF-5120-39/gcp_immuno/final_results/workflow_artifacts/costs/

export WORKFLOW_ID=b033e4be-8d5a-4bc1-9f6b-efa9387bd255

python3 ~/git/cloud-workflows/scripts/gb_estimate_billing.py $WORKFLOW_ID $GCS_BUCKET_PATH/workflow_artifacts/$WORKFLOW_ID/artifacts/metadata/ > costs.json