copilot api

This package holds the golang gRPC API definitions for copilot. There's one API used by Cloud Controller, another used by Istio Pilot.

The actual gRPC .proto files are in the protos subdirectory. To regenerate the golang code, run bin/dockerized-rebuild-proto from the gen folder.

We moved the .proto files in there to work around problems with Bazel in Istio.