[services] Backup - Add server reactor implementations - send log reactor
Summary:
Depends on D3467
Add implementation for the send log reactor
Test Plan:
cd services yarn run-backup-service
Reviewers: palys-swm, varun, geekbrother, jimpo
Reviewed By: palys-swm
Subscribers: ashoat, palys-swm, Adrian, atul, benschac
Differential Revision: https://phabricator.ashoat.com/D3516