refactor(rpc): node::proc_raft_join -> rpc::join::proc_raft_join

src/traft/rpc/join.rs

-use crate::traft::error::Error;
-use crate::traft::node;
-use crate::traft::FailureDomain;
-use crate::traft::Peer;
-use crate::traft::Result;
-use crate::traft::{InstanceId, ReplicasetId};
+use crate::traft::{error::Error, node, FailureDomain, InstanceId, Peer, ReplicasetId, Result};
 
 crate::define_rpc_request! {
     fn proc_raft_join(req: Request) -> Result<Response> {