lambda_http: Use http_body::Body for responses #409
Description
Since #406, lambda_http::Body implements http_body::Body. However, lambda_http::LambdaResponse only accepts lambda_http::Body as response body.
With this proposal, we could create a LambdaResponse from any Request<http_body::Body>, which means Lambda functions could return anything that implements this trait.
Drawbacks
Right now, we support receiving a serde_json::Value or other values that implement Into<Body> because we use a custom type.
I think this would no longer be possible if we accept a foreign trait, or would involve a bit more complexities on the implementation side.