[lib] make report id mandatory

Summary:
At this point id is added to existing reports, added on each creation and extracted before sending request to keyserver, so it's safe to make it mandatory as this will be needed to move reports to database.

Depends on D7913

Test Plan: N/A

Reviewers: tomek, michal

Reviewed By: tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7916