feat: path validation and typing

[simonireilly]

closes: #25

We need to support common things like:

• GET /users/{id} <= validate that id is a number
• GET /users?limit=10&offset=0
  • validate max limit of 50, min of 1
  • validate offset is number
• GET /users x-api-key: <string> - Validate API key is the specified string in the request

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Limitations, for now, we are going to aggressively focus on AWS API Gateway, because this is our use case.

Use the parameter spec to specify the validation: https://spec.openapis.org/oas/v3.1.0#parameterIn