Support configuration of unmanaged Kafka topics in `local.conf`

[thinkmorestupidless]

Is your feature request related to a problem? Please describe. I need to consume events from a Kafka topic not managed by Cloudflow and have that topic be the input for a streamlet. I can do this by providing config at deployment time but I have to be able to test this locally. Without having this configuration of topics with managed=no in local.conf I have to hardcode things into the blueprint file for testing.

Is your feature request related to a specific runtime of cloudflow or applicable for all runtimes? This applies to the integration with Kafka so applies to all runtimes

Describe the solution you'd like I'd like to be able to add a cloudflow.topics block in local.conf that provides all the features described in this section of the docs

Describe alternatives you've considered putting all the Kafka config into blueprint.con for testing and then pulling it out when building/deploying the app. That's a bit rubbish as a workflow, though.

Additional context None