[services] Backup - Add data hash to the log item

Summary:
Depends on D4277

linear task: https://linear.app/comm/issue/ENG-1288/properly-handle-the-dynamodb-item-size-limit

If we want to be able to move a log item's data dynamically after creation, from the database to the S3, we need to store the data hash in the backup log's database.

Test Plan: Services still build

Reviewers: palys-swm, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul, yayabosh

Differential Revision: https://phab.comm.dev/D4320