Repository transfer has to be confirmed, if user can not create repo for new owner (#14792)

* make repo as "pending transfer" if on transfer start doer has no right to create repo in new destination

* if new pending transfer ocured, create UI & Mail notifications

models/migrations/v174.go

@@ -0,0 +1,23 @@
+// 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 migrations
+
+import (
+	"xorm.io/xorm"
+)
+
+func addRepoTransfer(x *xorm.Engine) error {
+	type RepoTransfer struct {
+		ID          int64 `xorm:"pk autoincr"`
+		DoerID      int64
+		RecipientID int64
+		RepoID      int64
+		TeamIDs     []int64
+		CreatedUnix int64 `xorm:"INDEX NOT NULL created"`
+		UpdatedUnix int64 `xorm:"INDEX NOT NULL updated"`
+	}
+
+	return x.Sync(new(RepoTransfer))
+}