the config is like for swh-storage, so something like this:
journal_writer: cls: kafka args: brokers: "%{alias('swh::deploy::journal::brokers')}" prefix: "%{alias('swh::deploy::journal::prefix')}" client_id: "swh.indexer.storage.journal_writer.%{::swh_hostname.short}" producer_config: message.max.bytes: 1000000000
It's unclear what the prefix should be. swh.storage uses swh.journal.objects, we can either use that one too, or a new one, eg. swh.journal.indexed