Part of [[ https://linear.app/comm/issue/ENG-4269/implement-the-database-schema | ENG-4269 ]].
Removed all code related to the old database from the HTTP server part of the service. (gRPC still uses it).
Renamed `http/context.rs` to `http/errors.rs` because the only code left there is error handling.
Depends on D8458.