[services] Backup - Blob Put Client - Add helper functions

Summary:
Depends on D5005

Adding some helper function that will be used by the put client

Test Plan: backup builds

Reviewers: jon, tomek, varun, max

Reviewed By: jon, tomek

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D5006