Add `schema_extra` metadata to Pydantic schemas

[seanpreston]

FastAPI allows us to specify example data attributes to be picked up and auto documented by Swagger. We should use this in our externally facing Pydantic schemas. https://fastapi.tiangolo.com/tutorial/schema-extra-example/

[wiseaidev]

Hey @seanpreston and other ethyca fellas. It is hacktoberfest season, and I would like to work on this issue since I am already familiar with schema examples in fastapi. Therefore, this issue seems like easy to grab for me. Essentially, I need to go through all the schemas and add examples accordingly. However, for a faster review process, I am going to open a PR with 1 commit/schema file/folder. Also, are there any requirements on the value of each field, or i am good to add whatever value I want? That's pretty much it. Have a good day/night!