[services] Backup - Fix requests in proto file

Summary:
Depends on D3529

We need a user id in every request in the backup service, how else will we know where the request comes from?

Previously the user id was deeper in the authentication types but they were removed and we missed that we removed the user id as well.

Test Plan:

cd services
yarn run-backup-service

Reviewers: palys-swm, geekbrother, varun, jimpo, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3530