Validate, set, and coerce inputs based on OpenAPI spec

[ezwelty]

We have an extensive OpenAPI spec, so we should rely on it to perform a lot of boilerplate. There is a small ecosystem of packages that handles validation, setting default values, and casting to corrected types:

• https://www.npmjs.com/package/openapi-request-validator
• https://www.npmjs.com/package/openapi-default-setter
• https://www.npmjs.com/package/openapi-request-coercer