[Maintenance] Replace Bitnami Kafka with free SolDevelo alternative

[igor-soldev]

Hi team!

I noticed that internal/command/default.provisioners.yaml currently references bitnami/kafka. Since Bitnami images are now largely behind a paywall, I suggest switching to soldevelo/kafka (maintained by my team).

It is free to use, actively updated, and works as a drop-in replacement.

I can submit a quick PR to update this if you're interested!