[services] Tests - Add backup test logic

Summary:
Depends on D4251

Adding code for the backup test itself.

It does the following things:

• define starting data
• create a new backup and add attachments to it based on the starting data
• send logs and add attachments to them based on the starting data
• perform "pull backup" and save the results
• compare the obtained data with the starting data

Test Plan:

cd services
yarn run-integration-tests backup

Reviewers: palys-swm, varun

Reviewed By: palys-swm, varun

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

Differential Revision: https://phab.comm.dev/D4252