Split migrations folder (#21549)

There are too many files in `models/migrations` folder so that I split
them into sub folders.

models/migrations/v1_9/v83.go

@@ -0,0 +1,28 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package v1_9 //nolint
+
+import (
+	"code.gitea.io/gitea/modules/timeutil"
+
+	"xorm.io/xorm"
+)
+
+func AddUploaderIDForAttachment(x *xorm.Engine) error {
+	type Attachment struct {
+		ID            int64  `xorm:"pk autoincr"`
+		UUID          string `xorm:"uuid UNIQUE"`
+		IssueID       int64  `xorm:"INDEX"`
+		ReleaseID     int64  `xorm:"INDEX"`
+		UploaderID    int64  `xorm:"INDEX DEFAULT 0"`
+		CommentID     int64
+		Name          string
+		DownloadCount int64              `xorm:"DEFAULT 0"`
+		Size          int64              `xorm:"DEFAULT 0"`
+		CreatedUnix   timeutil.TimeStamp `xorm:"created"`
+	}
+
+	return x.Sync2(new(Attachment))
+}