Use python import machinery to find known studies

[mikix]

Previously, we assumed they'd be directories inside site-packages.

But in some cases (like pip install -e . in linux), that installs a .pth file that points at the real location.

So let's just ask Python where these known modules are.

Fixes #290

Checklist

• [x] Consider if documentation in docs/ needs to be updated
  • If you've changed the structure of a table, you may need to run generate-md
  • If you've added/removed core study fields that not in US Core, update our list of those in core-study-details.md
• [x] Consider if tests should be added
• [x] Update template repo if there are changes to study configuration in manifest.toml

[github-actions[bot]]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
2032	2019	99%	90%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
cumulus_library/cli.py	100%	🟢
TOTAL	100%	🟢

updated for commit: f9bc9d2 by action🐍