Move pydantic models to their respective module

[korikuzma]

Could also consider taking the pydantic models that are associated with specific modules (eg db connection args w/ the uta handler) and putting them directly into that module. The pattern of a distinct schemas.py module or group of modules is more suited to MVC-like web apps imho (where you have a models module, a views module, and a controller module), and while there are some models that are truly general-purpose and can't be placed anywhere else, others can probably be moved closer to where they're used.

Originally posted by @jsstevenson in #334 (comment)