Split migrations folder (#21549)

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

models/migrations/v1_10/v90.go

@@ -0,0 +1,18 @@
+// 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_10 //nolint
+
+import "xorm.io/xorm"
+
+func ChangeSomeColumnsLengthOfRepo(x *xorm.Engine) error {
+	type Repository struct {
+		ID          int64  `xorm:"pk autoincr"`
+		Description string `xorm:"TEXT"`
+		Website     string `xorm:"VARCHAR(2048)"`
+		OriginalURL string `xorm:"VARCHAR(2048)"`
+	}
+
+	return x.Sync2(new(Repository))
+}