Move some files into models' sub packages (#20262)

* Move some files into models' sub packages

* Move functions

* merge main branch

* Fix check

* fix check

* Fix some tests

* Fix lint

* Fix lint

* Revert lint changes

* Fix error comments

* Fix lint

Co-authored-by: 6543 <6543@obermui.de>

templates/swagger/v1_json.tmpl

@@ -18828,7 +18828,7 @@
           "$ref": "#/definitions/TimeStamp"
         }
       },
-      "x-go-package": "code.gitea.io/gitea/models"
+      "x-go-package": "code.gitea.io/gitea/models/activities"
     },
     "UserSettings": {
       "description": "UserSettings represents user settings",