TokenLoader replacement with Kafka

TokenLoader class has the same role as a consumer in Kafka. Research how to replace it with Kafka There are two options :
1) to have a Kafka consumer that will process the messages the same way as the TokenLoader
or
2) replace some of the business logic of TokenLoader with Kafka Streams and push to another Kafka topic the message with concrete tokens.

In the current implementation, MessageHolderWithVariantsConsumer consumes MessageHolderWithVariants and send it to TokenLoader#loadAndQueueTokenBatch

TODO subtasks need to be defined.