[services-lib] Add method to download blobs

Summary:
Part of ENG-4597.

This diff introduces a function that creates a download stream for blob and a few utilities.

Depends on D8777

Test Plan: Tested together with next diffs.

Reviewers: michal, jon

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8778