Integrate http4s WebSocket app with AWS Lambda API Gateway

[armanbilge]

Similarly to our existing http4s integration which allows to deploy an HttpApp as handler of AWS Lambda API Gateway events, it would be useful to have an integration for deploying a WebSocket app. Integrating with http4s would make it seamless to move applications between serverless and server deployments.

However, one important question is how the lifecycle is managed i.e. does the same Lambda instance handle the entirety of a WebSocket connection? If so, then we can be stateful across events and implement the handler with Stream/Pipe. Otherwise, I'm not entirely certain what the API should look like.