[serverless-offline-sqs] Support for maximumBatchingWindow

[tomusiaka]

Based on non-offline functionality and docu, it is possible to set maximumBatchingWindow. This sends MaximumBatchingWindowInSeconds attribute to SQS ReceiveMessage action. Offline that would be simulated using WaitTimeSeconds attribute in receiveMessage action. However, serverless-offline-sqs plugin seems to ignore that setting. Wait time is always 5 seconds, which appears to be hard-coded in the receiveMessage request.

[terozio]

This makes local testing super slow if you want to do something message per message when you always need to wait before the lambda function is triggered.