Add SetWithTTL to the Database interface

packages/database/interfaces.go

 package database
 
+import "time"
+
 type Database interface {
 	Set(key []byte, value []byte) error
+	SetWithTTL(key []byte, value []byte, ttl time.Duration) error
 	Contains(key []byte) (bool, error)
 	Get(key []byte) ([]byte, error)
 	ForEach(func(key []byte, value []byte)) error