Split migrations folder (#21549)

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

models/migrations/v1_15/v187.go

@@ -0,0 +1,48 @@
+// Copyright 2021 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_15 //nolint
+
+import (
+	"code.gitea.io/gitea/models/migrations/base"
+
+	"xorm.io/xorm"
+)
+
+func DropWebhookColumns(x *xorm.Engine) error {
+	// Make sure the columns exist before dropping them
+	type Webhook struct {
+		Signature string `xorm:"TEXT"`
+		IsSSL     bool   `xorm:"is_ssl"`
+	}
+	if err := x.Sync2(new(Webhook)); err != nil {
+		return err
+	}
+
+	type HookTask struct {
+		Typ         string `xorm:"VARCHAR(16) index"`
+		URL         string `xorm:"TEXT"`
+		Signature   string `xorm:"TEXT"`
+		HTTPMethod  string `xorm:"http_method"`
+		ContentType int
+		IsSSL       bool
+	}
+	if err := x.Sync2(new(HookTask)); err != nil {
+		return err
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+	if err := base.DropTableColumns(sess, "webhook", "signature", "is_ssl"); err != nil {
+		return err
+	}
+	if err := base.DropTableColumns(sess, "hook_task", "typ", "url", "signature", "http_method", "content_type", "is_ssl"); err != nil {
+		return err
+	}
+
+	return sess.Commit()
+}