Enable Kafka batch processing

[wagmarcel]

Kafka batch processing is not enabled in the current backend.
Problem:
This is reducing the performance of the backend since communicating with KairosDB creates a 3-5ms latency. Since Kafka mandates sequential processing this was reducing the backend to ~200Hz processing.
Enabling batching is removing this bottleneck since this allows to processing up to 1000 samples per KairosDB call.
The implementaion will be similar to https://memorynotfound.com/spring-kafka-batch-listener-example/