Use pydantic for all serialization

[Kilo59]

There are currently two layers of modeling for the location data.

Ideally, the pydantic response models should be the only domain models required for the location data.
However, to avoid a large re-design all at once it might be easier to improve and simplify the intermediate non-pydantic domain models.

https://github.com/Kilo59/coronavirus-tracker-api/blob/master/app/location/__init__.py#L8
https://github.com/Kilo59/coronavirus-tracker-api/blob/master/app/location/csbs.py#L5
https://github.com/Kilo59/coronavirus-tracker-api/blob/master/app/location/nyt.py#L5

At a minimum, these domain models should be updated so that they can easily be "deserialized" from their "serialized" versions. Which as of now they cannot 😦 .