feat: First POC on adding transactions to Actual via python API.

[bvanelli]

Features:

• Better handling of internal fields and mapping between pydantic attributes and database columns.
• Support conversion to protobuf for most models
• Implementation to create user files locally, run migrations, and upload them to actual server.
• Add context manager to Actual class

Refactors:

• Separating endpoints into their own file
• Changing all pydantic database attributes to pythonic versions

Docs:

• Improve documentation for most methods