Update Confluent.Kafka library to version 1.8.2

[jakob-nielsen-dfds]

Includes enhancements, fixes, and security updates since 1.5.3.

For details see:

• Version referenced: https://github.com/confluentinc/confluent-kafka-dotnet/releases/tag/v1.8.2
• Changes from 1.5.3 - 1.8.2: https://github.com/confluentinc/confluent-kafka-dotnet/releases