[services-lib] Let blob client use services token

Summary:
Changed blob client logic to use the new AuthorizationCredential enum instead of the more specific UserIdentity

Depends on D9243

Test Plan: Blob client works as before

Reviewers: michal, varun, jon

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9275