[lib] Add optional Authorization header to reports endpoint

Summary:
Part of ENG-6289.

Added a way to pass optional AuthMetadata to reports endpoint.
This header is optional because this endpoint should also work without any authentication.
Authentication gives us possibility to identify the user who is sending the report.

Depends on D10913

Test Plan: Tested together with the next diff.

Reviewers: tomek, michal

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D10930