Summary:
This is the basics of GO builds.
Will write up a document for this soon, when things stabalize a bit.

We also need to add some validation to make sure that the wrong proto library does not get used (we only use gogo)
and that it will auto-complete correctly in IDEs.

Test Plan:
```
make clean

make help

make build

bazel run //throwaway/golang-grpc-service/greeter_server:greeter_server

(in another window)
bazel run //throwaway/golang-grpc-service/greeter_client:greeter_client
```

Reviewers: kgandhi, michelle

Reviewed By: kgandhi

Maniphest Tasks: T2

Differential Revision: https://phab.corp.pixielabs.ai/D20

GitOrigin-RevId: 9360b845f7f291db517ed635c0f33644fd2ff480