storage: skip ApplyConfChange on rejected entry

When in a joint configuration, passing an empty conf change to
ApplyConfChange doesn't do the right thing any more: it tells
Raft that we're leaving the joint config. It's not a good idea
to try to tell Raft anything about a ConfChange that got rejected.
Raft internally knows that we handled it because it knows the applied
index.

This also adds a case match for ConfChangeV2 which is necessary to
route atomic replication changes (ConfChangeV2).

See etcd-io/etcd#11046

Release note: None

pkg/storage/replica_application_state_machine.go

@@ -998,10 +998,11 @@ func (sm *replicaStateMachine) maybeApplyConfChange(ctx context.Context, cmd *re
 			log.Fatalf(ctx, "unexpected replication change from command %s", &cmd.raftCmd)
 		}
 		return nil
-	case raftpb.EntryConfChange:
+	case raftpb.EntryConfChange, raftpb.EntryConfChangeV2:
 		if cmd.replicatedResult().ChangeReplicas == nil {
-			// The command was rejected.
-			cmd.confChange.ConfChangeI = raftpb.ConfChange{}
+			// The command was rejected. There is no need to report a ConfChange
+			// to raft.
+			return nil
 		}
 		return sm.r.withRaftGroup(true, func(raftGroup *raft.RawNode) (bool, error) {
 			raftGroup.ApplyConfChange(cmd.confChange.ConfChangeI)