[services] Backup - generate backup id

Summary:
Depends on D4099

https://linear.app/comm/issue/ENG-918/implement-generating-backup-id

Test Plan:
Run the blob service
Run the backup service
Use grpc-playground to make a call creating a new backup

Either log out the generated backup id or check in the database

Reviewers: palys-swm, ashoat

Reviewed By: palys-swm, ashoat

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

Differential Revision: https://phabricator.ashoat.com/D4028