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/backup/recipes/default.rb

@@ -28,6 +28,7 @@ template "#{backup_dir}/config.rb" do
   sensitive true
   variables s3_access_key_id: backup_data["s3_access_key_id"],
             s3_secret_access_key: backup_data["s3_secret_access_key"],
+            s3_endpoint: backup_data["s3_endpoint"],
             s3_region: backup_data["s3_region"],
             encryption_password: backup_data["encryption_password"],
             mail_from: "backups@kosmos.org",