Support consuming Kinesis' enhanced fanout for flink-connector-kinesis

AWS Kinesis enhanced fanout is a feature that allows consumers to consume a separated sub-stream without competing with other consumers. (https://docs.aws.amazon.com/streams/latest/dev/building-enhanced-consumers-api.html)

Yet, currently flink-connector-kinesis can only consume main streams, which may lead to tense competition.

A support for the enhanced fanout feature is quite useful for AWS users.