[Shared/docs] Update yarn codegen-grpc

Summary:
Update yarn workflow for updating codegen-grpc

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

Depends on D4992

Test Plan:

# should get re-generated
rm shared/protos/_generated/blob.grpc.pb.cc

cd shared
yarn codegen-grpc

# assert blob gets regenerated
git status # should be empty

Reviewers: atul, varun, abosh, max, karol

Reviewed By: max

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D4993