docs(overview): updates component descriptions

[PaulRMellor]

Documentation

Updates the overview content describing Kafka components to reduce the focus on ZooKeeper
Component diagram update to remove ZooKeeper is a placeholder.
A new diagram will replace it to organise the components better

Checklist

Please go through this checklist and make sure all applicable tasks have been done

• Write tests
• Make sure all tests pass
• Update documentation
• Check RBAC rights for Kubernetes / OpenShift roles
• Try your changes from Pod inside your Kubernetes and OpenShift cluster, not just locally
• Reference relevant issue(s) and close them after merging
• Update CHANGELOG.md
• Supply screenshots for visual changes, such as Grafana dashboards

[scholzj]

LGTM. Thanks.

[ppatierno]

I was wondering why we are anticipating these changes in the doc while ZooKeeper is still around. I mean, at some point, the doc would need additional changes because something like this "A KRaft-based Kafka cluster ....." will need to be fixed as just "A Kafka cluster ..." to make KRaft implicit because ZooKeeper was gone.

[scholzj]

@ppatierno My take ... more and more people now use KRaft. So I think making it gradually more prominent in the docs corresponds to it.