Enable Kerberos support for Kafka auth

[trickster]

Vector has complete librdkafka config support which enables Kerberos auth. Would like to have a similar feature or just Kerberos support in general for sources/sinks.

[Jeffail]

Hey @trickster, needs a bit of investigation but I think sarama might support kerberos now so this could be fairly quick to add, I've raised an issue #877.