I do not see those in the defaults.yaml.

For the brokers option, i see kafka::brokers.
The other i see only hard-coded prefix at other locations.

I think it's a a free form field.

I'm not entirely sure what this field should convey as information.

But as the module in the storage has been renamed to journal_writer.
Shan't we maybe rename it to swh.storage.journal_writer. to match it?
I know it's redundant in here but at runtime, not so much (probably heh ;)

I did not know we could do that, so thanks for highlighting me ;)