Paperclip is incompatible with ruby 3.0, move attachment logic to ActiveStorage

[Paperclip is deprecated](https://robots.thoughtbot.com/closing-the-trombone).
**Paperclip is incompatible with ruby 3.0.**
_For new projects, we recommend Rails' own [ActiveStorage](http://guides.rubyonrails.org/active_storage_overview.html)._

https://github.com/thoughtbot/paperclip/blob/master/MIGRATING.md