[BUG] Support multivalue query parameters

[johnboxall]

URLs may contain multivalue query parameters. That is a parameter with the same name may appear multiple times in a query string: ?q=123&q=abc.

As an example, SCAPI's product search API allows you to use the refine parameter multiple times to set a number of refinements on a search.

Today, multiple values are discarded and only the last value is available on Express code.

This is because the version of aws-serverless-express we're using doesn't correct forward the Lambda event to the Express server: CodeGenieApp/serverless-express#214

This issue only impacts code running on Managed Runtime, it doesn't appear locally, because we don't use the lib locally.

[bendvc]

Hey @johnboxall thank you for supporting the community, we've discussed this with the PM and we are looking to get this in to the next major version release. @natemarcus

[bfeister]

I've created a new bug for this unintentionally, but a customer is tracking the new one so we might close this as dupe... or just keep both ope

#1106

[bfeister]

#1106 Fixes this.