[IMPROVED] NRG: Clarify log when resetting WAL (#6938)

Usually `Resetting WAL state` is a prime indicator something went
horribly wrong with replication, and resetting is our last effort at
fixing things. Antithesis reports on this being logged so we can look
into it and fix the condition.

However, this also triggers if the WAL is empty, a leader gets elected
and stores a message that doesn't get quorum. Once a new leader is
elected and this entry without quorum gets removed, we'd also log
`Resetting WAL state` even though this is a normal condition. If we have
made no commits, it's safe to reset/clear the WAL. This PR changes the
log line to clarify this.

Relates to #6705

Signed-off-by: Maurice van Veen <[email protected]>

Author: neilalexander

server/raft.go

@@ -3259,7 +3259,11 @@ func (n *raft) truncateWAL(term, index uint64) {
 	n.debug("Truncating and repairing WAL to Term %d Index %d", term, index)
 
 	if term == 0 && index == 0 {
-		n.warn("Resetting WAL state")
+		if n.commit > 0 {
+			n.warn("Resetting WAL state")
+		} else {
+			n.debug("Clearing WAL state (no commits)")
+		}
 	}
 
 	defer func() {