Split migrations folder (#21549)

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

models/migrations/v1_18/v224.go

@@ -0,0 +1,28 @@
+// Copyright 2022 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_18 // nolint
+
+import (
+	"xorm.io/xorm"
+)
+
+func CreateUserBadgesTable(x *xorm.Engine) error {
+	type Badge struct {
+		ID          int64 `xorm:"pk autoincr"`
+		Description string
+		ImageURL    string
+	}
+
+	type userBadge struct {
+		ID      int64 `xorm:"pk autoincr"`
+		BadgeID int64
+		UserID  int64 `xorm:"INDEX"`
+	}
+
+	if err := x.Sync2(new(Badge)); err != nil {
+		return err
+	}
+	return x.Sync2(new(userBadge))
+}