FEATURE: Support private attachments when using S3 storage (#7677)

* Support private uploads in S3
* Use localStore for local avatars
* Add job to update private upload ACL on S3
* Test multisite paths
* update ACL for private uploads in migrate_to_s3 task

config/initializers/014-track-setting-changes.rb

@@ -34,6 +34,8 @@ DiscourseEvent.on(:site_setting_changed) do |name, old_value, new_value|
 
   Jobs.enqueue(:update_s3_inventory) if [:s3_inventory, :s3_upload_bucket].include?(name)
 
+  Jobs.enqueue(:update_private_uploads_acl) if [:prevent_anons_from_downloading_files].include?(name)
+
   SvgSprite.expire_cache if name.to_s.include?("_icon")
 
   if SiteIconManager::WATCHED_SETTINGS.include?(name)