Display when a repo was archived (#22664)

This adds the date a repo is archived to Gitea and shows it in the UI
and API. A feature, that GitHub has been [introduced
recently](https://github.blog/changelog/2022-11-23-repository-archive-date-now-shown-in-ui/).

I currently don't know how to correctly deal with the Date in the
template, as different languages have different ways of writing a date.


![grafik](https://user-images.githubusercontent.com/15185051/234315187-7db5763e-d96e-4080-b894-9be178bfb6e1.png)

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/migrations/v1_20/v255.go

@@ -0,0 +1,23 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_20 //nolint
+
+import (
+	"code.gitea.io/gitea/modules/timeutil"
+
+	"xorm.io/xorm"
+)
+
+func AddArchivedUnixToRepository(x *xorm.Engine) error {
+	type Repository struct {
+		ArchivedUnix timeutil.TimeStamp `xorm:"DEFAULT 0"`
+	}
+
+	if err := x.Sync(new(Repository)); err != nil {
+		return err
+	}
+
+	_, err := x.Exec("UPDATE repository SET archived_unix = updated_unix WHERE is_archived = ? AND archived_unix = 0", true)
+	return err
+}