Kinesis Connector to report millisBehindLatest metric

When reading from Kinesis streams, one of the most valuable metrics is "MillisBehindLatest" (see https://github.com/aws/aws-sdk-java/blob/25f0821f69bf94ec456f602f2b83ea2b0ca15643/aws-java-sdk-kinesis/src/main/java/com/amazonaws/services/kinesis/model/GetRecordsResult.java#L187-L201).

Flink should use its metrics mechanism to report this value as a gauge, tagging it with the shard id.