[Bug] API Gateway v2 cookies response should be array

According to API Gateway v2 payload 2.0 docs (https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-develop-integrations-lambda.html) the 'cookies' should be array.
And below code is current handling logic for it.

https://github.com/vendia/serverless-express/blob/671f914429e9708bfb1ee6ba76b5947a917592df/src/event-sources/aws/api-gateway-v2.js#L65-L67

However, with the latest express (v4.17.1).
When user set cookie using `res.cookie(name, value)`, it set 'set-cookie' header as string at first time.
and convert it as array when using `res.cookie(name, value)` more than once.

So, we should insert Array check logic, and convert it to array when it is not.

Plus,
If we didn't delete 'set-cookie' header in response, API gateway send 'set-cookie' header twice.
So, for gateway v2 and payload 2.0 we should delete 'set-cookie' header field.

Start in src/event-sources/aws/api-gateway-v2.js at the linked handling logic, and compare the response behavior when Express sets one cookie versus multiple cookies. Done means API Gateway v2 receives cookies as an array and the original set-cookie header is removed so it is not sent twice.

Scritto dal modello di indicizzazione a partire dal testo della issue.