This PR removes all external deps except gRPC. Or all external infrastructure.

The assumption here is go-micro is bloated by all these different plugins being included in the go mod. By leaning it out, people can find this even more valuable for their use cases. We may go on to include distributed systems primitives ourselves e.g raft consensus, gossip membership, federated kv store.

Ideally go-micro becomes a building block for the next generation of services. And go-plugins is the host to the external infrastructure plugins.