global: Move gRPC-related packages into common package hierarchy
We've grown quite a bunch of packages that provide various different
functionality in the context of gRPC. But it is not easy to identify
them as there is no common hierarchy for gRPC-related functionality.
We're thus introducing a new internal/grpc
package that will host
various bits and pieces related to gRPC.
Move packages that provide gRPC-related functionality into internal/grpc
.