Setting up custom config

**Is your feature request related to a problem? Please describe.**
I want to disable writing to a journal and I don't see how it can be done with helm charts. As far as I understood I need to do it here https://bookkeeper.apache.org/docs/reference/config/ but I don't see any ways how to create custom configs in pulsar helm charts.

**Describe the solution you'd like**
It would be good to show some examples in documentation how it can be done

**Describe alternatives you've considered**
Maybe I can use pulsar admin to disable writing to a journal but I'd rather know how to create custom configs using helm charts.