[lib/web/native] implement sending confirmation of processed message
Summary:
Confirmation after the message is processed.
Implementing only sending - the handling of confirmation will be implemented in the next goal 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. (cc. @marcin)
Test Plan: Manually add some messages and process them, check if confirmation is sent
Reviewers: tomek, marcin
Reviewed By: marcin
Subscribers: marcin, ashoat
Differential Revision: https://phab.comm.dev/D11731