kafka-c(): Publish messages to Apache Kafka (C implementation)

Starting with version 3.21, AxoSyslog can directly publish log messages to the Apache Kafka message bus, where subscribers can access them.

As of AxoSyslog version 3.21, the new C implementation of the kafka destination is available. The new implementation uses the librdkafka client and has several advantages, such as scalability, more efficient memory usage and simpler setup. The options of this implementation are compatible with those of the old Java implementation.