Split migrations folder (#21549)

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

models/migrations/v1_13/v154.go

@@ -0,0 +1,56 @@
+// Copyright 2020 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_13 //nolint
+
+import (
+	"code.gitea.io/gitea/modules/timeutil"
+
+	"xorm.io/xorm"
+)
+
+func AddTimeStamps(x *xorm.Engine) error {
+	// this will add timestamps where it is useful to have
+
+	// Star represents a starred repo by an user.
+	type Star struct {
+		CreatedUnix timeutil.TimeStamp `xorm:"INDEX created"`
+	}
+	if err := x.Sync2(new(Star)); err != nil {
+		return err
+	}
+
+	// Label represents a label of repository for issues.
+	type Label struct {
+		CreatedUnix timeutil.TimeStamp `xorm:"INDEX created"`
+		UpdatedUnix timeutil.TimeStamp `xorm:"INDEX updated"`
+	}
+	if err := x.Sync2(new(Label)); err != nil {
+		return err
+	}
+
+	// Follow represents relations of user and their followers.
+	type Follow struct {
+		CreatedUnix timeutil.TimeStamp `xorm:"INDEX created"`
+	}
+	if err := x.Sync2(new(Follow)); err != nil {
+		return err
+	}
+
+	// Watch is connection request for receiving repository notification.
+	type Watch struct {
+		CreatedUnix timeutil.TimeStamp `xorm:"INDEX created"`
+		UpdatedUnix timeutil.TimeStamp `xorm:"INDEX updated"`
+	}
+	if err := x.Sync2(new(Watch)); err != nil {
+		return err
+	}
+
+	// Collaboration represent the relation between an individual and a repository.
+	type Collaboration struct {
+		CreatedUnix timeutil.TimeStamp `xorm:"INDEX created"`
+		UpdatedUnix timeutil.TimeStamp `xorm:"INDEX updated"`
+	}
+	return x.Sync2(new(Collaboration))
+}