Confirmation after the message is processed.
Implementing only sending - the handling of confirmation will be implemented in the next goal [Broadcasting information to peers](https://linear.app/comm/issue/ENG-7398/[may]-broadcasting-information-to-peers).
This is the logic for a non-primary device where we could confirm the message right after processing DB ops. For primary we will have to wait until the backup log is uploaded, this is tracked in [Backup client changes for syncing data & log upload](https://linear.app/comm/project/persist-backup-logs-in-sqlite-a3819ef08eaf). (cc. @marcin)
Depends on D11730, D11729