[Examples/Tests] Replace Bitnami Kafka with free SolDevelo alternative

[igor-soldev]

Hi team!

I noticed that multiple files (including Containerlab examples, Docker Compose, and tests) currently reference bitnami/kafka. Since Bitnami images are now largely behind a paywall, I suggest switching to soldevelo/kafka (maintained by my team).
Link: https://hub.docker.com/r/soldevelo/kafka

It is free to use, actively updated, and works as a drop-in replacement. It is fully compatible with your existing configurations, so the examples will continue to work out of the box.

I can submit a PR to update these references across the repo if you're interested!