refactor(instance): extract mod instance

src/args.rs

src/governor/cc.rs

src/governor/mod.rs

src/governor/plan.rs

src/instance.rs

src/main.rs

src/replicaset.rs

src/storage.rs

src/traft/error.rs

src/traft/mod.rs

src/traft/network.rs

src/traft/node.rs

src/traft/rpc/expel.rs

src/traft/rpc/join.rs

src/traft/rpc/update_instance.rs

src/traft/topology.rs