Migrations - Add support for package imports

[techgerm]

Issue: #11

Helpful resources on the topic:

• https://stackoverflow.com/questions/50884100/using-importlib-to-dynamically-import-modules-containing-relative-imports
• https://napuzba.com/a/import-error-relative-no-parent

[maroux]

This is fine but does that mean you're unable to use spanner-orm CLI tool ? If so, maybe look into how alembic does it - it definitely works fine with the structure you've described..

[techgerm]

Correct, in order to get the scanner-cli tool to work like alembic it looks like we'd have to make it search for an env.py and program the spanner-cli tool to inject its dependencies from there.

I can create a separate issue on this if you'd like so at least it's a known issue. The good thing is we at least present one solution for packaged projects with the migration executer.

[maroux]

separate issue sounds good 👍