Provides a client that can be used to connect to and interact with
the transport service in `lib/srv/transport`. The client abstracts
the fact that a gRPC stream is being used for the `net.Conn` created
by `DialCluster` and `DialHost`.
This also moves `lib/utils/grpc/stream` to `api/utils/grpc/stream`
so that the client and server can make use of the same stream
abstractions.
Part of #19812
