[lambda_http] It would be helpful if the `aws_lambda_events/builders` feature were exposed through `lambda_http`

[dcormier]

To be able create instances of some of the types exposed via lambda_http::aws_lambda_events, it would help if the builders feature from aws_lambda_events was exposed.

In my specific case, I'm trying to create an aws_lambda_events::apigw::ApiGatewayProxyResponse instance to assert that the expected value was returned in a test. As it stands right now, I have to create use ApiGatewayProxyResponse::default() then separately set the fields I need.

Related: #1060

[jlizen]

Glad to have a pass-through builders feature, would you want to open a PR?