Merge remote-tracking branch 'origin/raft-pre-vote' into raft-pre-vote

# Conflicts:
#	raft-compat/go.mod
#	raft-compat/go.sum
#	raft-compat/prevote_test.go
#	raft-compat/testcluster/cluster.go
#	raft.go
#	raft_test.go

Author: dhiaayachi

commands.go

@@ -92,6 +92,7 @@ type RequestVoteRequest struct {
 	// transfer. It is required for leadership transfer to work, because servers
 	// wouldn't vote otherwise if they are aware of an existing leader.
 	LeadershipTransfer bool
+	PreVote            bool
 }
 
 // GetRPCHeader - See WithRPCHeader.
@@ -113,6 +114,9 @@ type RequestVoteResponse struct {
 
 	// Is the vote granted.
 	Granted bool
+
+	// Is it a preVote response
+	PreVote bool
 }
 
 // GetRPCHeader - See WithRPCHeader.