[Services] Update backup to reference new proto location

Summary:
Update backup to reference the new protobuf
file locations.

https://linear.app/comm/issue/ENG-1231

Test Plan:

nix develop
cd services/backup
rm -rf build && mkdir build && cd build && cmake .. && make -j

Backup CI gate passes

Reviewers: atul, karol, abosh, max

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D5043