[services] Tests - Backup - Calculate a real hash for backups/logs

Summary:
Depends on D4636

Calculating and sending real sha512 hash instead of some mocked bytes when creating a new backup and sending logs

Test Plan:
term 1

cd services
yarn run-blob-service-in-sandbox

term 2

cd services
yarn run-backup-service-in-sandbox

term 3

cd services
yarn run-integration-tests backup

check in the database that you have real hashes instead of something like ABCD

Reviewers: varun, tomek, ashoat

Reviewed By: tomek, ashoat

Subscribers: ashoat, tomek, adrian, atul, abosh

Differential Revision: https://phab.comm.dev/D4667