[reports] Move HTTP-specific service code

Summary:
Moving code around. The service.rs became too big, so kept only reports business logic there,
and moved HTTP-specific code to http/service.rs

Depends on D12448

Test Plan: cargo check

Reviewers: will, varun, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12451