[services-lib] Add BlobInfo utility type

Summary:
Adds a type that represents the information of an owned blob. This is useful for storing the blob reference in DDB

Depends on D8777, D8790

Test Plan: Tested later with real usage.

Reviewers: michal, jon

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8791