Add script to parse wdl files for steps and file inputs

[lvreynoso]

Description

Adds a script intended to extract information from each stage's wdl file, namely what steps are in it, what inputs and outputs are in each step, and what the actual filenames are. This information will be used in the Pipeline Visualization for samples run on the SFN workflow.

Notes

Part of a larger work to adapt the Pipeline Viz. The script is meant to be called by Open3 when used by a ruby file, with the wdl data passed in through stdin.

Tests

• Tested with the host_filter, non_host_alignment, postprocess, and experimental wdl files currently in use and on S3.
• Automated test written using unittest and kept in test/python

[tfrcarvalho]

Quick comment to not forget to describe how you tested it. Also, add the skip QA labels.