Add simple update checker to Gitea (#17212)

Add simple update checker to Gitea (#17212)

* Add simple update checker to Gitea

* update struct and remove comments

* fix lint

* Update custom/conf/app.example.ini

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: delvh <dev.lh@web.de>
* Update custom/conf/app.example.ini

Co-authored-by: delvh <dev.lh@web.de>
* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: delvh <dev.lh@web.de>
* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: Steven <61625851+justusbunsi@users.noreply.github.com>
* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

* Update modules/cron/tasks_extended.go

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
* Update custom/conf/app.example.ini

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
* take PR feedback into account and display banner on admin dashboard for alerts

* Add more detailed message

* placate lint

* update per feedback

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Steven <61625851+justusbunsi@users.noreply.github.com>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>