Add TypeScript support for ALB related types

[vandrade-git]

This library has ALB integration but current TypeScript types do not reflect this.

For example the API#run method does not accept an ALBEvent type meaning that if someone wants to be extremely correct the fix is something like the following:

async function handler(event: ALBEvent, context: Context): Promise<any> {
  return api.run(event as unknown as APIGatewayProxyEvent, context);
}

This PR aims to fix this.

[naorpeled]

LGTM!
Thank you for your contribution :)