Adapt maxRecords parameter in the getRecords call to optimize bytes read from Kinesis

The Kinesis connector currently has a constant value set for maxRecords that it can fetch from a single Kinesis getRecords call. However, in most realtime scenarios, the average size of the Kinesis record (in bytes) changes depending on the situation i.e. you could be in a transient scenario where you are reading large sized records and would hence like to fetch fewer records in each getRecords call (so as to not exceed the 2 Mb/sec per shard limit on the getRecords call). 

The idea here is to adapt the Kinesis connector to identify an average batch size prior to making the getRecords call, so that the maxRecords parameter can be appropriately tuned before making the call. 

This feature can be behind a ConsumerConfigConstants flag that defaults to false.