[Shared] Copy protos to shared/protos, adjust CMake

Summary:
Initial move of protobuf files

The files are copied to the desired end state so that I can update the references in later revisions.

The CMakeLists.txt was pruned of the grpc client project.

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

Test Plan:

nix develop
cd shared/protos
rm -rf build && mkdir build && cd build && cmake .. && make -j
# builds 4 grpc projects

Reviewers: atul, abosh, max, karol, tomek

Reviewed By: max, karol, tomek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D4992