[Protos] Move GetKeyserverInfo to authtenticated service

Summary:
We should only be issuing one-time keys to authenticated
devices. Move this to the authenticated service.

Part of https://linear.app/comm/issue/ENG-4445

Depends on D7691

Test Plan: N/A. Protobuf review

Reviewers: varun, bartek

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8605