[Services] Update blob to reference new directory

Summary:
Update blob references to protobuf directory

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

Depends on D4996

Test Plan:

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

Reviewers: atul, abosh, varun, max, karol, tomek

Reviewed By: atul, max, karol, tomek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D4998