v2.3.1: health check fixes (#45)
* refactor: use Kafka interfaces instead of implementations * fix: align compileJava and compileKotlin tasks target * feat: make it possible to register multiple instances of the same check where it makes sense * fix(DatabaseConnectionHealthCheck): return `Unhealthy` when connection is invalid * fix(MongoConnectionHealthCheck): make the health check usable with both sync and async clients