[blob-service] Add S3 helpers, improve logs

Summary:
Minor convenience functions for S3 path type conversioons and some more logs

Depends on D8440

Test Plan: Will be tested later in the stack

Reviewers: michal, jon, varun, patryk

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8441