Add Typeshare support for Python

[hculea]

Thanks to the prior work of @adriangb: https://github.com/1Password/typeshare/pull/25

This will be picked up in the coming weeks. Would already appreciate a provisional review with high-level feedback on design!

[Lucretiel]

Doing some review, sorry for the delay. I'd like to ask for a high-level description in this MR for how this integration works, with especial focus on how structs are handled (in particular how the JSON <-> struct boundary is handled).