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It is especially useful if there are outdated labels that should no longer be used without deleting the label entirely.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 The time when a label has been archived will be stored in the DB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/swagger/v1_json.tmpl

@@ -17057,6 +17057,11 @@
           "x-go-name": "Exclusive",
           "example": false
         },
+        "is_archived": {
+          "type": "boolean",
+          "x-go-name": "IsArchived",
+          "example": false
+        },
         "name": {
           "type": "string",
           "x-go-name": "Name"
@@ -18001,6 +18006,11 @@
           "x-go-name": "Exclusive",
           "example": false
         },
+        "is_archived": {
+          "type": "boolean",
+          "x-go-name": "IsArchived",
+          "example": false
+        },
         "name": {
           "type": "string",
           "x-go-name": "Name"
@@ -19479,6 +19489,11 @@
           "format": "int64",
           "x-go-name": "ID"
         },
+        "is_archived": {
+          "type": "boolean",
+          "x-go-name": "IsArchived",
+          "example": false
+        },
         "name": {
           "type": "string",
           "x-go-name": "Name"