Allow to archive labels (#26478)

## Archived labels 

This adds the structure to allow for archived labels.
Archived labels are, just like closed milestones or projects, a medium to hide information without deleting it.
It is especially useful if there are outdated labels that should no longer be used without deleting the label entirely.

## Changes

1. UI and API have been equipped with the support to mark a label as archived
2. The time when a label has been archived will be stored in the DB

## Outsourced for the future

There's no special handling for archived labels at the moment.
This will be done in the future.

## Screenshots

![image](https://github.com/go-gitea/gitea/assets/80308335/208f95cd-42e4-4ed7-9a1f-cd2050a645d4)

![image](https://github.com/go-gitea/gitea/assets/80308335/746428e0-40bb-45b3-b992-85602feb371d)

Part of https://github.com/go-gitea/gitea/issues/25237

---------

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/issue/labels/edit_delete_label.tmpl

@@ -33,6 +33,16 @@
 				<div class="desc gt-ml-2 gt-mt-3 gt-hidden label-exclusive-warning">
 					{{svg "octicon-alert"}} {{.locale.Tr "repo.issues.label_exclusive_warning" | Safe}}
 				</div>
+				<br>
+			</div>
+			<div class="field label-is-archived-input-field">
+				<div class="ui checkbox">
+					<input class="label-is-archived-input" name="is_archived" type="checkbox">
+					<label>{{.locale.Tr "repo.issues.label_archive"}}</label>
+				</div>
+				<i class="gt-ml-2" data-tooltip-content={{.locale.Tr "repo.issues.label_archive_tooltip"}}>
+					{{svg "octicon-info"}}
+				</i>
 			</div>
 			<div class="field">
 				<label for="description">{{.locale.Tr "repo.issues.label_description"}}</label>