Redirect on changed user and org name (#11649)

* Add redirect for user

* Add redirect for orgs

* Add user redirect test

* Appease linter

* Add comment to DeleteUserRedirect function

* Fix locale changes

* Fix GetUserByParams

* Fix orgAssignment

* Remove debug logging

* Add redirect prompt

* Dont Export DeleteUserRedirect & only use it within a session

* Unexport newUserRedirect

* cleanup

* Fix & Dedub API code

* Format Template

* Add Migration & rm dublicat

* Refactor: unexport newRepoRedirect() & rm dedub del exec

* if this fails we'll need to re-rename the user directory

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/api/v1/user/helper.go

@@ -0,0 +1,36 @@
+// Copyright 2021 The Gitea Authors.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package user
+
+import (
+	"net/http"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/context"
+)
+
+// GetUserByParamsName get user by name
+func GetUserByParamsName(ctx *context.APIContext, name string) *models.User {
+	username := ctx.Params(name)
+	user, err := models.GetUserByName(username)
+	if err != nil {
+		if models.IsErrUserNotExist(err) {
+			if redirectUserID, err := models.LookupUserRedirect(username); err == nil {
+				context.RedirectToUser(ctx.Context, username, redirectUserID)
+			} else {
+				ctx.NotFound("GetUserByName", err)
+			}
+		} else {
+			ctx.Error(http.StatusInternalServerError, "GetUserByName", err)
+		}
+		return nil
+	}
+	return user
+}
+
+// GetUserByParams returns user whose name is presented in URL (":username").
+func GetUserByParams(ctx *context.APIContext) *models.User {
+	return GetUserByParamsName(ctx, ":username")
+}