[services-lib][blob-client] Use Bytes instead of Vec<u8>

Summary:
Partially overlaps with D8964 - we should use Bytes instead of Vec<u8> for blob data to avoid unnecessary allocations.

Also added the bytes dependency to services-lib and re-exported it.

Depends on D8786

Test Plan: Tested together with the next diff

Reviewers: michal, jon

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8974