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/v184.go

@@ -0,0 +1,72 @@
+// 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 (
+	"context"
+	"fmt"
+
+	"code.gitea.io/gitea/models/migrations/base"
+	"code.gitea.io/gitea/modules/setting"
+
+	"xorm.io/xorm"
+)
+
+func RenameTaskErrorsToMessage(x *xorm.Engine) error {
+	type Task struct {
+		Errors string `xorm:"TEXT"` // if task failed, saved the error reason
+		Type   int
+		Status int `xorm:"index"`
+	}
+
+	// This migration maybe rerun so that we should check if it has been run
+	messageExist, err := x.Dialect().IsColumnExist(x.DB(), context.Background(), "task", "message")
+	if err != nil {
+		return err
+	}
+
+	if messageExist {
+		errorsExist, err := x.Dialect().IsColumnExist(x.DB(), context.Background(), "task", "errors")
+		if err != nil {
+			return err
+		}
+		if !errorsExist {
+			return nil
+		}
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	if err := sess.Sync2(new(Task)); err != nil {
+		return fmt.Errorf("error on Sync2: %w", err)
+	}
+
+	if messageExist {
+		// if both errors and message exist, drop message at first
+		if err := base.DropTableColumns(sess, "task", "message"); err != nil {
+			return err
+		}
+	}
+
+	switch {
+	case setting.Database.UseMySQL:
+		if _, err := sess.Exec("ALTER TABLE `task` CHANGE errors message text"); err != nil {
+			return err
+		}
+	case setting.Database.UseMSSQL:
+		if _, err := sess.Exec("sp_rename 'task.errors', 'message', 'COLUMN'"); err != nil {
+			return err
+		}
+	default:
+		if _, err := sess.Exec("ALTER TABLE `task` RENAME COLUMN errors TO message"); err != nil {
+			return err
+		}
+	}
+	return sess.Commit()
+}