logger: add logger to bbolt

Signed-off-by: Mustafa Elbehery <melbeher@redhat.com>

Author: Elbehery

logger.go

@@ -1,11 +1,11 @@
 package bbolt
 
+// See https://github.com/etcd-io/raft/blob/main/logger.go
 import (
 	"fmt"
 	"io"
 	"log"
 	"os"
-	"sync"
 )
 
 type Logger interface {