Message export: Fix job progress calculation (#21925)

* use posts count instead of job duration to calculate progress

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

store/sqlstore/post_store.go

@@ -2272,6 +2272,20 @@ func (s *SqlPostStore) AnalyticsPostCount(options *model.PostCountOptions) (int6
 		query = query.Where(sq.Eq{"p.DeleteAt": 0})
 	}
 
+	if options.ExcludeSystemPosts {
+		query = query.Where("p.Type NOT LIKE 'system_%'")
+	}
+
+	if options.SinceUpdateAt > 0 {
+		query = query.Where(sq.Or{
+			sq.Gt{"p.UpdateAt": options.SinceUpdateAt},
+			sq.And{
+				sq.Eq{"p.UpdateAt": options.SinceUpdateAt},
+				sq.Gt{"p.Id": options.SincePostID},
+			},
+		})
+	}
+
 	queryString, args, err := query.ToSql()
 	if err != nil {
 		return 0, errors.Wrap(err, "post_tosql")