Kafka metrics missing for authentication/authorization problems

[ffendt]

Hi there,

when playing around with Kafka connections I found a missing metric entry when having authentication problems with the used Kafka service provider.

There are success metrics for the categories dispatched, filtered and mapped but there is missing a failure on the published category.

When looking into the logs if found out that KafkaPublisherActor logs a message when it encounters such problems. However, it does not look as if it would be easy to add the correct metric since the called method does not know the context in which an error occured. It seems as if we would need to rewrite (and enhance) some functionality that is currently part of the alpakka kafka library.