feature: support replicaset_id

• Choose it in the topology module if it's not provided in a JoinRequest.
• Persist in raft_group space.
• Respond with an error if JoinRequest contains different replicaset_id.
• In JoinResponse it's transferred automatically.

Part of #51 (closed)

src/traft/mod.rs

@@ -69,7 +69,7 @@ pub struct Peer {
     pub peer_address: String,
     pub voter: bool,
     pub instance_id: String,
-    // pub replicaset_id: String,
+    pub replicaset_id: String,
     pub instance_uuid: String,
     // pub replicaset_uuid: String,
     /// `0` means it's not committed yet.