Configurable idle time between getRecords requests to Kinesis shards

Currently, the Kinesis consumer is calling getRecords() right after finishing previous calls. This results in easily reaching Amazon's limitation of 5 GET requests per shard per second. Although the code already has backoff & retry mechanism, this will affect other applications consuming from the same Kinesis stream.

Along with this new configuration and the already existing `KinesisConfigConstants.CONFIG_SHARD_RECORDS_PER_GET`, users will have more control on the desired throughput behaviour for the Kinesis consumer.