Fix up and improve Kafka integration tests

[Jeffail]

The integration tests (https://github.com/Jeffail/benthos/tree/master/lib/test/integration) for Kafka are awful, mostly because Kafka is an utter pain to run. They need to be updated and fixed up, ideally so that they also run on macOS (with docker running in a VM) and with settings for SASL and ideally TLS being tested also.

[mangatmodi]

How about using TestContainers? I have been using Kafka's TestContainer in Mac and it is working well.

[jarri-abidi]

Where exactly are the integration tests for kafka @Jeffail? The link in the description returns 404.

[Jeffail]

Hey @jarri-abidi they're within https://github.com/benthosdev/benthos/tree/main/internal/impl/kafka now, since raising this issue I've introduced tests around Redpanda which work much better but ideally I'd still like to have tests against an official Kafka container.