add parameters for offsetConsumer in KafkaIO.read()

Add an option in KafkaIO.read() to avoid using `offsetConsumer`. 

What's the problem:

When security is enabled, function `KafkaUnboundedReader.updateLatestOffsets()` always fails with lots of WARN log.

What's the cause:

`offsetConsumer` uses a mocked `ConsumerConfig.GROUP_ID_CONFIG`, and it doesn't work as expected when security is enabled. In our case, `ConsumerConfig.GROUP_ID_CONFIG` is the key to validate whether this consumer is approved.

What's the solution:

Add an option to disable `offsetConsumer` by developers;

What's the side effect:

With `offsetConsumer` disabled, backlog is unknown.

rangadi any comments?