Migrate S3 backups from AWS, fix automatic cleanups

The cleanups were broken in that every single archive was also copied to
a shared folder and never deleted from there.

Co-authored-by: Greg Karékinian <greg@karekinian.com>

site-cookbooks/kosmos_gitea/recipes/backup.rb

@@ -8,5 +8,6 @@
 unless node.chef_environment == "development"
   # backup the data dir and the config files
   node.override["backup"]["archives"]["gitea"] = [node["gitea"]["working_directory"]]
+  node.override['backup']['s3']['keep'] = 2
   include_recipe "backup"
 end